Effects of Fono lexis on Children With Phonological Disorders

Abstract

Children with phonologically based speech sound disorders (SSDs) often experience difficulties in phonological perception, production, and awareness. Integrated intervention approaches address these domains simultaneously and promote links between phonology and orthography. The Fonolexis program, based on an integrated approach to the treatment of phonological disorder, was recently developed and validated for European Portuguese; however, evidence regarding its effectiveness in children with SSD is still limited. This study aimed to evaluate the effects of the Fonolexis program in preschool children with phonologically based SSD using a pre–post pilot design. Twelve preschool-age children (n = 12) received 24 intervention sessions delivered by the same speech-language therapist, organized into three blocks of eight sessions. Pre- and post-intervention assessments were conducted by another speech-language therapist. Outcome measures included percentage of correct consonants (PCC), occurrence of phonological processes, and phonological inventory. Results showed a substantial improvement in PCC (p = .002), a reduction in targeted phonological processes, an expansion of the phonological inventory, and generalization to untreated words. These findings support the positive effects of the Fonolexis program in preschool children with SSD.

Keywords

phonologically based speech sound disorder integrated intervention Fonolexis program

Introduction

Early childhood is a time of rapid growth and development when children produce sounds intelligibly, thus enabling them to become competent communicators (Lousada et al., 2012; McLeod et al., 2022). However, this acquisition process is not easy for some children who show difficulties in producing some sounds (McLeod et al., 2022). The umbrella term to describe these difficulties is speech sound disorder (SSD; McLeod et al., 2022).

Speech sound disorder is a very common neurodevelopmental disorder in childhood. The estimated prevalence of SSD ranges from 1.06% to 20.5% (McLeod et al., 2022), with this variability largely reflecting differences in study methodologies, sample characteristics, data collection methods, and definitions used across international research. In Portugal, prevalence studies are scarce and, in most cases, on a small scale. Data from a recent study showed that of the 203 children screened, 5.9% had articulation SSD and 14.3% had phonological SSD (Fernandes & Lousada, 2022).

With the exception of articulation-based SSD, which involves substitutions or distortions of sounds in isolation, words and sentences, during imitation, elicitation and spontaneous speech tasks primarily associated with underlying motor-based difficulties in speech production, the other SSDs always involve some degree of difficulty in phonology. These are known as phonologically based SSD, characterized by the presence of typical and/or atypical phonological processes without motor-based difficulties. For most of these children, the disorder is of unknown origin (Dodd, 2005; McLeod et al., 2022; Ramalho & Lousada, 2022).

Children with phonologically based SSD may have difficulties in perception (Hearnshaw et al., 2018), production (Lousada et al., 2013), and phonological awareness (Burgoyne et al., 2019), and there may be impairment in segmental and prosodic units (Lousada et al., 2022). These difficulties usually have a negative impact on the intelligibility of their speech (Hearnshaw et al., 2018; Lousada et al., 2019).

These disorders can also have social and emotional implications throughout life (Fernandes & Lousada, 2022). Some examples of this impact can be related to difficulties in interacting with peers, making and maintaining friendships, feeling sad and frustrated with SSD (McLeod et al., 2022). This negative impact is more prominent when children do not receive speech-language therapy at an early age.

Children with SSD, when compared with their peers with typical development, are more likely to drop out of school and may also have difficulties getting and/or keeping a job (McLeod et al., 2022). This disorder not only affects the individual, but can also affect family members considering the SSD may lead to frustration, misunderstandings, and emotional stress within everyday interactions at home. Parents and caregivers often experience concern or anxiety about their child’s development and future academic or social outcomes. In this way, the effects of SSD can extend beyond the individual to influence family dynamics, relationships, and overall well-being (McLeod et al., 2022). However, when intervention is provided during the preschool years, the prognosis is generally favorable (Bishop et al., 2017).

Oliveira et al. (2015) reported that most speech-language therapists (SLTs) in Portugal combined several approaches in their intervention with children with SSD. In 2018, a model of intervention in SSD emerged that was divided into five categories (see Table 1), according to the area where change is expected to occur and which indeed is being targeted in the intervention (Wren et al., 2018).

Table 1.

Model of Intervention in SSD (Wren et al., 2018).

Category	Target of the intervention
Environmental approaches	Encompasses intervention approaches that make use of everyday interactions, rather than speciﬁc directed activities, to promote change in a child’s speech-sound system.
Auditory-perceptual approaches	Target the child’s perceptual skills as a means to induce change in speech output. Activities are used to increase exposure to the sounds being targeted, such as focused auditory stimulation, and discrimination tasks.
Cognitive-linguistic approaches	Engage the child in higher-level, metalinguistic processing by explicitly targeting conscious awareness of their own speech production. The child is encouraged to reflect on and monitor their phonological output, and this increased awareness is systematically used to facilitate phonological change.
Production approaches	Aims to effect change through performance of oro-motor tasks, guidance on phonetic placement or manner, imitation and drills.
Integrated approaches	Combine two or more of the other categories.

Multiple investigations have explored the effectiveness of treatments in the Integrated Intervention Approaches category (Wren et al., 2018), which is the focus of the treatment involved in this research. Siemons-Lühring et al. (2021) studied a sample of 32 preschool children in which the group that received intervention with an integrated approach showed a higher percentage of correct consonants (PCC) and a large reduction in the occurrence of phonological processes, after 15 sessions, compared with the control group. Gillon (2000) found that children between the ages of 5 and 7 who received an integrated intervention approach showed significant gains in phonological awareness, reading development, and articulation of speech sounds, reaching levels similar to those of children with typical development.

In Portugal, there are few intervention studies on SSD (Reis et al., 2023), with only two randomized controlled trials (RCTs; Jesus et al., 2019; Lousada et al., 2013) and one quasi-experimental study (Pedro et al., 2014). Pedro et al. (2014) compared the effectiveness of two phonological-based intervention approaches, ‘Parents and ChildrenTogether’ – an Integrated Approach (Bowen, 2009) and the ‘Phonological awareness therapy’ – a Cognitive-Linguistic Approach (Gillon & McNeill, 2007). Using a group of six children ages between 5;0 and 6;1 and diagnosed with SSD, Pedro et al. (2014) reported that both approaches proved beneficial in improving both the production and the syllabic awareness of the children. In addition, phonological awareness therapy led to an improvement in the children’s phonemic awareness skills.

Lousada et al. (2013) conducted an RCT with Portuguese children, which included 14 children with phonologically based SSD ages between 4 years and 6 years and 7 months. A comparison was made between the effectiveness of an integrated phonological approach (n = 7, which included phonological awareness therapy (Gillon & McNeill, 2007), together with auditory discrimination activities (Lancaster, 2008)) and Traditional Articulation Therapy, a Production Approach (n = 7). The intervention included three blocks of eight sessions each. At the end of each intervention block, a test was used to generalize the target to words not used during the intervention. The results showed that children who were treated with an Integrated Phonological Intervention showed a more significant improvement than children treated only with Traditional Articulation Therapy in severity measures such as the PCC (primary outcome measure), percentage of occurrence of phonological processes and phonetic inventory, as well as in the target generalization test to words not used in the intervention.

Lousada et al. (2014) investigated changes in measures of intelligibility for the children from the Lousada et al. (2013). In this second study, 21 adults analyzed the children’s intelligibility. The results showed significant improvements in the intelligibility of single words and continuous speech only in children treated with the Integrated Phonological Approach.

Jesus et al. (2019) compared the effectiveness of an integrated digital approach (using tablets) with the physical version of cardboard activities in 22 children with phonologically based SSD. Both types of intervention showed improvements in PCC and phonemes produced correctly after the intervention. However, the impact on the percentage of correct vowels was only observed in the group that used the digital version. The changes recorded were significantly greater after the intervention, in both approaches, showing that the improvement resulted directly from the program. In addition, both groups showed high levels of generalization, with more than 60% of participants demonstrating transfer of the results to untrained words (Jesus et al., 2019).

Siemons-Luhring et al. (2021) evaluated the effectiveness of a program that also follows an integrated approach (PhonoSens). Thirty-two children, ages between 3 years and 5 months and 5 years and 5 months with SSD, were randomly assigned to two groups: a treatment group and a control group. The treatment group showed a greater improvement in PCC and a greater reduction in phonological processes after 15 therapy sessions compared with the control group (Siemons-Lühring et al., 2021).

Recently, Fonolexis (a structured tabletop intervention program) was developed for European Portuguese (EP)-speaking children, a program that follows the principles of an Integrated Phonological Approach with different intervention activities to promote auditory discrimination skills, production, and phonological awareness (including syllabic, intrasyllabic, and segmental awareness). These activities are aimed at children of preschool or early school age. A requirement for the implementation of Fonolexis is that the children have difficulties in the area of phonology, either a diagnosis of phonologically based SSD or a Language Development Disorder (DLD) with marked difficulties in the phonological domain (Rocha et al., 2025).

However, to date, there have been no studies analyzing the effects of Fonolexis on children with phonologically based SSD who speak EP. Thus, the main aim of this study is to determine the effects of Fonolexis on the speech production of preschool children with phonologically based SSD. The research question for the present study was: What are the effects of the Fonolexis program on children ages between 4 years and 6 months and 6 years with phonologically based speech sound disorders?

Method

Sample

Given the aim of the study, a pre-post pilot study was carried out. The sample included 12 children between the ages of 4 years and 6 months and 6 years, with phonologically based SSD. The following inclusion criteria were considered: (a) having a phonologically based SSD, diagnosed by a speech and language pathologist; (b) being ages between 4 years and 6 months and 6 years; and (c) having EP as their native language. Children were excluded when they had: (a) comorbidities (e.g. articulation-based disorder) and (b) difficulties in other areas of language (semantics, morphosyntax, and pragmatics). The children were recruited by SLTs, but none of the children had any concurrent therapy during this research.

Data Collection Instruments

The data collection instruments used were a Sociodemographic Questionnaire and the Phonetic-Phonological Test/Teste Fonético-Fonológico-ALPE (TFF-ALPE; Mendes et al., 2013).

Sociodemographic Questionnaire

A questionnaire was developed to characterize the children taking part in the study. Data collected included gender, age, and presence/absence of a diagnosis of phonologically based SSD.

TFF-ALPE

This instrument assesses phonetic-phonological skills (Lousada et al., 2012; Mendes et al., 2013). The TFF-ALPE assesses the ability to produce EP consonants, consonant clusters, and oral and nasal vowels in different word positions. Production is achieved by naming a set of images. The test is standardized for EP-speaking children ages between 3 years and 0 months and 6 years and 11 months (N = 768) and has good psychometric characteristics of validity and reliability (Lousada et al., 2012). The internal consistency, analyzed using Cronbach’s alpha, was .961. The interobserver reliability values were higher than 82%, and the intraobserver reliability values were higher than 93% (Lousada et al., 2012).

The lexical items included in the TFF-ALPE instrument were pre-tested to ensure that they were part of the expressive vocabulary of children ages 3 years and older. When children were unable to name the images spontaneously, semantic cues were provided in accordance with the standardized procedures of the assessment instrument. The data obtained with TFF-ALPE consisted of International Phonetic Alphabet transcriptions of each child’s productions and allowed for the calculation of different outcome measures: PCC, percentage of occurrence of phonological processes, and phonological inventory.

Data Collection Procedures

This study received approval from the Health Ethics Committee of the Fernando Pessoa Foundation Teaching Hospital (Opinion No. 05/2024). Authorization was requested via email. The children’s parents were provided with a set of documents, sent in paper format via the SLTs as well as information about the aim of the study and the procedures. Voluntary participation was requested and, after clarification and agreement to participate, the legal representatives were asked to sign the Informed Consent Form. Data collection took place between July 2024 and April 2025, during which time the initial assessments, intervention, and reassessment of each child were carried out.

Pre-Treatment Assessment

An initial assessment was carried out by an SLT using the TFF-ALPE test (Mendes et al., 2013). After this assessment, individual intervention sessions were carried out.

Generalization Task

The generalization task of the trained sound or phonological process to five non-intervention words was administered at the end of each intervention block. This task determined whether the child generalized the targeted speech skill and provided important insight into the impact of intervention on a child’s phonological system (Lousada et al., 2013). Pictures were used to elicit a spontaneous production.

Post-Treatment Assessment

At the end of the third block, the participants were reassessed using the TFF-ALPE, to understand the impact of Fonolexis on the participants’ production. A SLT, unaware of the specific aim of the study, conducted both the first assessment and the reassessment (after three intervention blocks). An author analyzed all data. A second co-author independently analyzed the assessment data to select intervention targets. Any discrepancies between the two researchers were discussed and resolved until a consensus was reached.

Intervention

Purpose

The Fonolexis program includes activities to promote auditory discrimination skills, production, and phonological awareness (including syllabic, intrasyllabic, and segmental awareness). In each session of each block, the SLT selects one activity for auditory discrimination and another activity that allows intervention on production and also phonological awareness.

Training of Administrators of the Intervention

The SLTs should read the manual of the Fonolexis before implementation. Regarding this study, the first author (a SLT) administered the Fonolexis to all the children.

Dosage of the Intervention

The SLTs select the number of blocks (each block with eight sessions) depending on the number of target sounds for each child. For each intervention block, a phonological process with target sounds was selected, based on the following criteria (a) frequently used processes: phonological processes with an occurrence of more than 40% were primarily chosen for the intervention; (b) the effect that phonological processes have on speech intelligibility; (c) the stimulability of sounds; and (d) the stages of normal phonological development. For this study, 24 intervention sessions were carried out, divided into three blocks, each with eight intervention sessions, once a week.

Treatment Procedures

The program includes six auditory discrimination activities with minimal pairs, with pictures for each target. For example, in the Maze activity (see Figure 1), the SLT presents the child with a maze with two possible paths and asks them to draw the path that leads to one of the items. The SLT selects the cards from the minimum pair to be worked on and places them on the maze board. For example, for the minimal pair ‘[dosɨ]/ [dozɨ]’, the instruction is ‘Draw the path from the cat to the sweet [dosɨ]’, contrasts with ‘Draw the path from the cat to the twelve [dozɨ]’.

Figure 1.

Example of the picture used for this Maze activity.

The program also includes 14 activities to work on phonological awareness and production, with 12 different stimuli for each target. The Fonolexis include stimuli for all consonants in all syllabic positions. For example, to work on the production and phonological awareness of the /z/ sound (target sound) in the Sudoku activity, the child should try to ensure that the stimuli are not repeated in the rows and columns of the game. In this way, they will discover which items are missing for each letter and name them (production). They should mention which items have the sound being worked on (phonemic awareness). The SLT use the following instruction: ‘Let’s play Sudoku (see Figure 2). The images cannot be repeated in the rows and columns. At the end, you must circle all the images you found with the sound /z/ and name them’.

Figure 2.

Example of the picture used for Sudoku for the target /z/ sound, with words zangão (male honeybee), Zé (Portuguese name of a boy), and Reza (praying).

Treatment Stimuli for Auditory Discrimination Activities With Minimal Pairs

Some criteria were used to select the stimuli for the activities with minimal pairs in Fonolexis, and whenever possible, mono- or disyllabic words were used. Different minimal pairs with minimal and maximal oppositions were also considered to intervene in the different contrasts at the level of the point of articulation, mode of articulation, and voicing. Some pairs of words with a contrast between consonant and semivowel, syllable with filled coda versus syllable with empty coda and simple attack versus branched attack were also used (Rocha et al., 2025).

Treatment Stimuli for Phonological Awareness and Production Activities

To select the stimuli for this activities, only mono- and disyllabic words were considered, preferably with a simple syllabic structure (with the exception of words with the segments /l/ and /ɾ/ in branched attack and coda and /ʃ/ in coda), so that they could be used at an early stage of the intervention. The target segments were considered in different word positions (initial, medial, and final, if applicable; Rocha et al., 2025). The word accent variable was also taken into account, since this variable sometimes influences production (Ramalho, 2017). Thus, the target segments for intervention were included in unstressed and stressed syllables.

Content Validation

Content validation of the Fonolexis stimuli had already been carried out with a panel of six experts (SLTs). Taking the experts’ suggestions into account, some images were reformulated and stimuli replaced. Subsequently, the Fonolexis intervention program was validated, again with a panel of six experts (SLTs with experience in intervening with children with phonologically based SSD). For both validation panels, the content validity index value was 1, which means that the words and illustrations used in the program have content validity (Rocha et al., 2025).

Analysis Procedures

The data collected with the TFF-ALPE (International Phonetic Alphabet Transcriptions of each child) were analyzed by the Automatic Phonological Analysis Tools (APAT; Saraiva et al., 2017). Automatic Phonological Analysis Tools is a validated phonological analysis tool that phonetically transcribes and calculates different outcome measures that were used in this study: PCC (primary outcome measure), percentage of occurrence of phonological processes, and phonological inventory – secondary outcomes (Saraiva et al., 2017).

The data (pre- and post-values of PCC and percentage of occurrence of phonological processes) were then entered into IBM SPSS Statistics 29.0.2.0 software and analyzed using descriptive and inferential statistics. Given the small size of the sample, the Wilcoxon test for paired samples (a non-parametric statistical measure) was used. Inferential statistical analysis was carried out with a significance level of α = .05.

To assess the magnitude of the intervention’s effect, the effect size (r) was calculated according to the formula proposed by Rosenthal, based on the Z statistic from the Wilcoxon test: $r = \frac{z}{\sqrt{N}}$ . The interpretation of the r value followed the criteria proposed by Cohen (1992), which consider small (≈ 0.1), medium (≈ 0.3), and large (≥ 0.5) effects.

Results

This section is organized as follows: (a) Primary outcome (PCC) obtained in both assessment moments; (b) Secondary outcomes obtained in both assessment moments; and (c) Generalization obtained after the three blocks of intervention.

The average age of the participants in this study was 70.58 months, and eight of them (66.67%) were male.

Primary Outcome

The PCC obtained in the pre-intervention assessment ranged from 47.42% to 89.69% (average = 69.85%). In the post-intervention assessment, the PCC ranged from 69% to 100% (average = 83.58%; see Figure 3).

Figure 3.

PCC results (%) obtained in pre- and post-intervention evaluations.

Table 2 shows the PCC results analyzed at two different times: before and after the intervention. The results of the Wilcoxon test revealed a significant difference (p = .002) in the PCC values before and after the intervention with the Fonolexis program. The value of Cohen’s r was 1.38, representing a large effect size.

Table 2.

PCC Results Obtained in the Pre- and Post-Intervention Assessments.

	PCC (%)
Descriptive statistics	Pre-intervention	Post-intervention	Difference pre and post
Mean	69.85	83.58	13.73
Min–Max	47.42–89.69	69–100	7–23
Standard deviation	10.82	9.00

Children who had low initial PCC values, such as RS (around 50%), showed considerable improvements, reaching values close to 70% after the intervention. Participants such as LM and DM, who had a mild disorder with PCC of 85% and 90%, respectively, showed further improvements, reaching 100%, and were therefore discharged from speech therapy.

Secondary Outcomes

Table 3 shows the percentages of occurrence of the phonological processes and the phonological inventory obtained in the assessments carried out before and after the intervention with Fonolexis. According to Yavas et al. (1991), a segment is acquired by a child when it is produced in 86% of the cases in which it can occur, thus forming part of the child’s phonological inventory (Yavas et al., 1991). In most cases, the children added targeted and untargeted segments. However, for some children (CM, LM, DM, and GC), only the segments that have been targeted in therapy were added.

Table 3.

Percentage of Occurrence of Phonological Processes and Phonological Inventory in the Pre- and Post-Intervention Assessments for Each Child.

Children	Pre-intervention	Phonological inventory	Post-intervention	Added segments
CM (5;4)	GL (27.3%); DEV (46.7%); SL (3.6%); FCD (70%)*; ICD (1.16%); CR (100%); OS (33.33%)	/p, t, k, b, d, g, m, n, ɲ, f, s, ʃ, v, ʎ, ʀ/	GL (7%); DEV (0%); SL (2%); FCD (40%); ICD (1%); CR (84%); OS (33.33%)	/z, ʒ, l/
LM (6;6)	GL (10.9%); DEV (46.7%); FCD (26.7); CR (78.9%)*;	/p, t, k, b, d, g, m, n, ɲ, f, s, ʃ, v, l, ɾ, ʎ, ʀ/	No phonological process	/z, ʒ/
TF (6;7)	GL (43.6%); DEP (94.1%); DEV (40%)*; FCD (70%); CR (100%);	/p, t, k, b, d, g, m, n, ɲ, f, s, v, ʀ/	GL (24%)*; DEP (0%) DEV (0%) FCD (40%); ICD (2%); CR (84%);	/ʃ, z, ʒ, l/
SR (6;1)	GL (16.4%); OCL (2.2%); FRON (3.3%); PAL (16.7%); DEV_OCL (4%); SV (2%); SL (1.8%); FCD (36.7%); ICD (7.1%); CR (68.4%); MON (11.1%); OS (33.33%)*;	/p, t, k, d, m, f, ʃ, ʒ/	GL (20%); OCL (0%); FRON (0%); PAL (0%); DEV OCL (0%); SV (0%); FCD (13%)*; ICD (1%); CR (63%); MON (0%); OS (0%);	/b, g, n, ɲ, s, v, z, ʀ/
LF (6;1)	GL (29.1%); FRON (3.3%); DEP (5.9%); BACK (3.9%); DEV (40%); FCD (30%); ICD (2.4%); CR (73.7%)*; MIS (26.32%)	/p, t, k, b, g, m, n, ɲ, f, s, ʃ, v, ɾ, ʀ/	GL (20%); FRON (0%); BACK (0%); DEV (0%); FCD (10%); ICD (0%); CR (26%); MIS (0%)	/d, z, ʒ/
RJ (6;5)	GL (32.7%); OCL (2.2%); FCD (66.7%); ICD (2.4%); CR (100%); OS (33.33%)*; MIS (5.26%)	/p, t, k, b, d, g, m, n, ɲ, f, s, ʃ, v, z, ʒ, ʎ/	GL (20%); OCL (0%); FCD (20%); ICD (0%); CR (84%); OS (0%); MIS (0%)	/ɾ, ʀ/
MA (4;2)	GL (29.1%); DEV (20%); SV (0.7%); FCD (86.7%); ICD (4%); CR (94.7%); OS (33.33%)*;	/p, t, k, b, d, g, m, f, v, ʀ/	GL (38%); DEV (0%); SV (0%); FCD (43%)*; ICD (0%); CR (84%); OS (0%)	/n, ɲ, s, ʃ, z, ʒ/
PO (6;8)	GL (38.2%); OCL (4.4%); DEP (52.9%); FCD (96.7%); ICD (2.4%); CR (100%); OS (100%)*;	/p, t, k, b, d, g, m, n, ɲ, f, s, z, ʀ/	GL (38%); OCL (0%); DEP (6%); FCD (3%); ICD (0%); CR (37%); OS (0%)	/ʃ, v, ʒ, ɾ/
SJ (5;4)	GL (27.3%); DEP (17.7%); BACK (3.9%); DEV (6.7%); SV (0.7%); FCD (86.7%); ICD (7.1%); CR (100%); OS (66.67%)*;	/p, t, k, b, n, ɲ, f, s, z, ʀ/	GL (38%); DEP (0%); BACK (0%); DEV (0%); SV (0%); FCD (20%)*; ICD (0%); CR (42%); OS (0%)	/d, g, m, ʃ, v, ʒ, ɾ/
RS (6;1)	GL (36.4%); OCL (17.4%), FRON (36.7%); DEP (5.9%); DEV_OCL (8%); DEV (6.7%); SV (0.7%); SL (1.8%); FCD (76.7%)*; ICD (3.2%); CR (100%); MON (11.1%); OS (33.33%);	/p, t, b, d, m, n, ɲ, ʃ, v, ʀ/	GL (35%); OCL (2%); FRON (3%); DEP (5.9%); DEV OCL (0%); DEV (27%); SV (0%); SL (0%) FCD (50%)*; ICD (3%) CR (84%); MON (11%); OS (67%);	/k, g, f, s/
DM (5;8)	GL (16.4%); OCL (2.2%); FCD (26.7%); CR (36.8%)*;	/p, t, k, b, d, g, m, n, ɲ, f, s, ʃ, v, z, ʒ, ʀ/	GL (0%); OCL (0%); FCD (0%); CR (0%); DEV_OCL (6%)	/l, ɾ/
GC (4;11)	GL (30.9%); DEV (46.7%); FCD (70%)*; ICD (4%); CR (100%); OS (100%);	/p, t, k, b, d, g, m, n, ɲ, f, s, ʃ, v, ʀ/	GL (24%); DEV (0%); FCD (43%); ICD (2%); CR (84%); OS (100%)	/z, ʒ/

Abbreviations for phonological processes used in the Table: FRON = Fronting; DEP = Depalatalization; OCL = Occlusion; FCD = final consonant deletion; BACK = Backing; CR = Cluster Reduction; SL = Substitution of liquids; GL = gliding of liquids; ICD = initial consonant deletion; MON = Monophthongization; OS = Omission of /ɾ/ segment in simple onset; DEV = devoicing; DEV_OCL = Occlusive devoicing; MIS = metathesis; SV = Vowel substitution. The phonological processes that were the target of intervention are marked with the * symbol. The segments that have been intervened upon and added are in bold.

The results indicated a reduction in the percentage of occurrence of the various phonological processes after the intervention, especially in those who were the target of treatment (see Table 3). For example, for child CM, there was a reduction from 46.7% to 0% in the target phonological process ‘devoicing’; a reduction from 27.3% to 7% in the target phonological process ‘gliding of liquids’ and a reduction from 70% to 40% in the target phonological process ‘final consonant deletion’. However, in certain cases, there was a slight increase in the percentage of phonological processes. A detailed analysis indicated that this was due to an overall improvement in speech (Lousada et al., 2013): two children (MA, SJ) showed an increase in the occurrence of semivocalization of liquids (GL, from 29.1% to 38% in MA and from 27.3% to 38% in SJ), since, in the pre-intervention assessment, they performed Initial Consonant Deletion (ICD), of some segments, including liquids, simplifying the syllabic structure to ‘V’ instead of ‘CV’ (e.g. telephone, in the pre-intervention assessment they said [tɨsɨsɨsɨ]; in the pre-intervention assessment, they said [tɨfɔnɨ]; after intervention, it became [tɨwɨfɔnɨ]). Thus, with the intervention, the ICD process disappeared, and the children began to replace the liquid with a semivowel, using a more complex syllabic structure compared with the pre-intervention period. In addition, in the pre-intervention period, they resorted to omitting the /l/ segment in coda and in branching attacks. After the intervention, they semivocalized the /l/ segment in the positions mentioned above (e.g. bucket went from [badɨ] to [bawdɨ] and bicycle went from ‘bikɛtɐ’ to [bisikwɛtɐ]).

In addition, in one of the children (RS), there was an increase in the occurrence of the devoicing process (DEV) from 6.7% to 27%, since, before the intervention, the child produced few fricative consonants and in a low percentage (e.g., ʃ, v). With the intervention, RS began to produce more fricatives (e.g., s), which resulted in an increase in the DEV process, as occurs in typical development (Mendes et al., 2013).

Generalization Test

The results of the generalization test make it possible to assess whether the child has generalized the target segment to other words not used during the intervention. This data provides valuable information about possible changes in the child’s phonological system and is an essential element in analyzing the effectiveness of the therapeutic intervention (Baker & McLeod, 2004; Lousada et al., 2012). Given that the intervention was divided into three blocks, each with different aims, a generalization test was applied after each intervention block (see Figure 4).

Figure 4.

Percentage of correct production in generalization test after each block.

Generalization After the First Block of Intervention

The results showed that 91.2% (n = 11) of the children demonstrated impressive levels of generalization (100%). The exception to this performance was RS who generalized to 60% of the words that were not worked on directly in the intervention (see Figure 4).

Generalization After the Second Block of Intervention

The results of the generalization test after the second intervention block revealed that all the children generalized to untargeted words. Three children (25%; RJ, RS, GC) generalized to the intervention target pattern to 80% of the words that had not been worked on in therapy, while the other nine children (75%) generalized to all the words that had not been the target of intervention (see Figure 4).

Generalization After the Third Block of Intervention

After the third intervention block, the results of the generalization test indicated that seven children (58.3%; CM, TF, LF, RJ, MA, SJ, RS) demonstrated generalization of the target pattern to 60% of the words that had not been used in the intervention. Three children (25%; SR, PO, GC) achieved a generalization rate of 80%, while two (16.7%; LM, DM) produced the target sound in all the words not worked on in the intervention (100%; see Figure 4).

Discussion

The aim of this study was to evaluate the effects of a phonological intervention program, Fonolexis, on preschool children with phonologically based SSD. The results obtained show substantial improvements in the oral production of the children who took part in the study, indicating the positive effects of the intervention implemented with Fonolexis. These findings should be considered preliminary due to the sample size and the design. However, the improvements observed in oral productions in this study are in line with scientific evidence presented in previous studies using integrated phonological-based approaches (Jesus et al., 2019; Siemons-Lühring et al., 2021; Wren et al., 2018).

In this study, eight (66.67%) of the 12 participants were male. This is in line with Ceron et al. (2017) and Lousada et al. (2013), who showed a higher prevalence of phonological SSD in males in different age groups.

Primary Outcome

The pre-intervention PCC values of the study participants ranged from 47.42% to 89.69%, which is below what is expected for typical development. Children between 4;6 and 5;0 have an average PCC of 95.1% (Jesus et al., 2015). The intervention proved to be effective both for children with more severe difficulties and for those with milder phonological disorders. Analysis of the data shows a consistent increase in PCC values (primary outcome measure) in all the children after the intervention, which is in line with other previous studies (Jesus et al., 2019; Lousada et al., 2019; Pedro et al., 2014; Siemons-Lühring et al., 2021). The generalized improvement in PCC suggests a positive evolution in the children’s phonological system. These changes indicate a reduction in phonological processes and also an increase in the phonological inventory (Siemons-Lühring et al., 2021).

Secondary Outcomes

Analysis of the occurrence of phonological processes at pre- and post-intervention revealed a substantial reduction in processes such as CR, FCD, and DEV, among others. In the initial pre-intervention assessment, some processes had occurrence values of over 70% (e.g., the child PO had 96.7% in the phonological process FCD), compromising the intelligibility of his speech. However, after the intervention, many of these processes were eliminated or drastically reduced (e.g. in this PO child, the phonological process FCD was reduced to 3%). These results corroborate other previous studies (Jesus et al., 2019; Siemons-Lühring et al., 2021).

The child LM (6;6), for example, used to perform several phonological processes (GL, DEV, FCD, and CR), and after the intervention, his PCC is 100%, that is, after using Fonolexis, he didn’t use any phonological process in his production, which represents a substantial gain in phonological acquisition. It was also possible to verify the acquisition of new segments in the phonological inventory of all the children. This result is also in line with the study by Lousada et al. (2013).

Generalization Task

In addition to the gains observed in PCC, the data from this study reveal relevant results in relation to generalization tests. The ability to generalize is a relevant criterion for assessing the effectiveness of phonological intervention (Baker & McLeod, 2004).

All the children achieved substantial levels of generalization in all three blocks, in words not trained during the intervention, indicating that the segments worked on during the application of Fonolexis were acquired and produced spontaneously in new contexts. This generalization indicates that the child was able to integrate the phonological rules trained during the intervention, demonstrating the ability to apply the knowledge acquired in the different blocks autonomously (Baker & McLeod, 2004). The generalization results after the third block were slightly lower but always above 50%. These results show increased levels of generalization comparatively to those obtained in a previous study by Lousada et al. (2013).

The children performed slightly differently from one another, supported by the evidence that children with SSD are a heterogeneous population (Rvachew & Matthews, 2024). This different performance between blocks for the same children is also in line with what was observed in the study by Lousada et al. (2013).

Comparison Between Studies

Considering the absence of a control group, a critical analysis of the results obtained in this study will also be made through the comparison with the study carried out by Lousada et al. (2013), since it is a very similar study for EP in terms of intensity of intervention, integrated phonological approach, and outcome measures.

The results obtained in terms of PCC showed that the children in the study by Lousada et al. (2013) had lower PCC pre- and post-intervention compared with those in the present study and also had a slightly greater improvement between the pre-intervention and post-intervention PCC values (see Figure 5).

Figure 5.

Comparison between PCC from the present study and the study by Lousada et al. (2013).

The fact that the children in the study by Lousada et al. (2013) had a lower average age (62.21 months) than those in the present study (70.58 months) may explain the difference in initial PCC as well as the greater improvement between pre-intervention PCC and post-intervention PCC. This interpretation is supported by evidence indicating that early intervention is associated with better prognostic outcomes (Otaiba et al., 2009).

In addition to the age difference already mentioned, the diagnosis is different in the two studies. In the present study, the sample was constituted by children with phonological SSD and in Lousada et al. (2013) the sample was composed by children with a diagnosis compatible with DLD with phonological alterations as well as alterations in other linguistic domains, which may also justify the differences in the children’s initial PCC.

Both studies showed a relevant improvement in PCC after the intervention, as well as a reduction in phonological processes. The activities in both studies follow an integrated approach and are similar to each other. This is a factor that demonstrates the positive effect of integrated approaches on children with phonologically based SSD.

Limitations and Future Directions

This study has some limitations. The sample size is reduced, and the methodology used did not include a control group, due to the constraints of the institution where the participants were recruited. Intervention studies with a control group and larger samples are, therefore, needed to be able to generalize the results obtained.

Conclusion

The results of this study have important clinical implications for speech-language pathologist intervention. The evidence that intervention with the Fonolexis program contributed to a substantial increase in PCC and a decrease in the occurrence of phonological processes suggests the program’s effectiveness and is a contribution to evidence-based practice in children with phonologically based SSD. The application of this type of program in a clinical or school context can promote speech intelligibility, self-esteem and, consequently, the academic and social performance of children (McLeod et al., 2022).

Footnotes

ORCID iDs

Daniela Lopes

Marisa Lousada

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported through the ESF – European Social Fund and FCT – Fundação para a Ciência e a Tecnologia, I.P., within RISE-Health (UID/06397/2025) and within the scope of the project RISE (LA/P/0053/2020) and IEETA (UID/00127).

Declaration of Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

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