Abstract
There is mixed consensus on the long-term academic impacts of Early Childhood Education (ECE) programs on children’s outcomes. While some studies show sustained benefits from preschool through to secondary school, others report that early gains, particularly in literacy, fadeout by grade 1. One explanation proposed in the literature is that this fadeout may result from ECE programs emphasis on constrained literacy skills over unconstrained literacy skills. This scoping review examined how the terms constrained and unconstrained literacy skills are defined, interpreted, and applied in early childhood education research, and the extent to which researchers find these concepts useful. Findings from 19 peer-reviewed and 22 grey literature articles revealed five main categories: benefits of ECE services, evaluation, family involvement, teacher perception, and skill development and assessment. The review illustrated inconsistent definitions and variable application of the constrained/unconstrained framework yet also highlighted its conceptual value for explaining different developmental trajectories in literacy skills. Overall, findings suggest that unconstrained literacy skills may fade out at a slower rate than constrained literacy skills, underscoring the need for ECE programs to adopt a balanced and comprehensive literacy approach that supports both types of skills.
Keywords
Introduction
The development of strong literacy skills in early childhood is critical for academic success, laying the foundations for future learning, employment opportunities and overall life outcomes. High quality early childhood education (ECE) programs have been identified as playing a critical role in fostering children’s learning and development, including literacy skills. Research has demonstrated that participation in ECE programs yields positive impacts on children’s social-emotional development and academic skills, including early literacy development (Melhuish et al., 2015; Weiland & Yoshikawa, 2013). These early gains have also been associated with long term academic attainment (McCoy et al., 2017). The wealth of evidence supporting the benefits of attendance in ECE programs has contributed to the growing provision of funded preschool programs globally (OECD, 2017). However, research has found mixed results regarding the long-term, sustained impacts of these programs on children’s outcomes as they progress through formal schooling (Harrison et al., 2012; Magnuson et al., 2004; Sylva et al., 2004). This phenomenon of initial gains followed by diminishing effects over time has been referred to as “fadeout” (Claessens & Garrett, 2014; Lipsey et al., 2018; Taggart et al., 2015).
To better understand the fadeout effect, researchers have applied the concept of constrained and unconstrained skills (Paris, 2005), specifically within the domain of literacy. Constrained constructs include letter identification, phonics, and spelling, as these skills have a finite scope that can be fully mastered (McCormick & Mattera, 2022). In contrast, unconstrained skills include constructs such as vocabulary and reading comprehension, which have no ceiling and can be developed throughout the lifespan (McCormick & Mattera, 2022). The distinction between constrained and unconstrained literacy skills may help to understand fadeout patterns, as constrained skills taught in ECE programs may reach a ceiling effect, while unconstrained skills continue to develop (Paris, 2005). However, research examining constrained versus unconstrained skills in ECE is still emerging. Studies have found that ECE programs tend to focus more heavily on constrained literacy skills, such as letter recognition and phonics (Markowitz & Ansari, 2020; Walter & Lippard, 2017).
However, the extent to which ECE programs prioritise constrained skills is rather nuanced with a growing body of research highlighting tensions between educators’ commitments to play-based pedagogies and policy, curriculum or family pressures that emphasise early phonics and a focus on other constrained skill development (Campbell, 2015). Some educators express concern about the push-down of phonics curriculums from school-based approaches into ECE programs, which threaten play-based literacy learning, while some feel compelled by school-readiness expectations, growing parental pressure and assessment frameworks to prioritise explicit systematic phonics methods (Campbell, 2018; Mantei et al., 2022). In addition to these pressures, in states and countries where high-stakes testing is used as a measure of teaching quality, a narrowing of the curriculum to focus on constrained skills can result (Snow & Matthews, 2016; Whittingham et al., 2021). Many of the widely used assessments for measuring young children’s development, such as language and literacy abilities, tend to capture constrained skills as these are easier to measure (McCormick & Mattera, 2022). There is a mismatch between the skills taught, those measured in evaluations of the impact of ECE programs on children’s outcomes, and the skills needed for long-term academic success, which may contribute to fadeout effects.
High quality ECE programs that feature high levels of instructional support – characterised by promoting an understanding of everyday concepts through analysing, creating, and integrating previous knowledge; facilitating thinking by providing information and asking open-ended questions; and modelling language through frequent conversations using advanced vocabulary and language – may be more effective in supporting the development of unconstrained skills alongside constrained skills (McCormick et al., 2021; Tayler, 2016). While unconstrained skills, including language skills (e.g., vocabulary and discourse skills) and general knowledge are accepted by researchers and educators as critical for literacy success, they are more challenging to influence in practice (Snow & Matthews, 2016).
Given the importance of fostering both constrained and unconstrained skills for children’s long-term academic success, there is a need to better understand how these skills are conceptualised and measured in ECE settings. Current research may have disproportionately focused on evaluating the benefits of constrained skills promoted by ECE programs, potentially leading to an incomplete picture of the full benefits of ECE programs on children’s academic outcomes, especially given that unconstrained skills are more likely to be sustained in the later years. As the conceptual framework of constrained and unconstrained skills is relatively new, it is important to explore how this framework is being applied and understood in the context of ECE research. This scoping review aims to address this gap by exploring the following research question: How are the terms constrained and unconstrained skills defined, interpreted, and applied in early childhood education research, and to what extent do researchers find these concepts useful for studying early childhood literacy learning?
Methods
This study is a scoping review of published literature on unconstrained and constrained literacy skills in ECE. The methods used were informed by the guidance for scoping reviews provided by Peters et al. (2015) and rapid review method guidance by Garritty and colleagues (2021). The following steps were taken according to their recommendations: (1) identification of the review purpose, research question and scope of the enquiry; (2) definition of eligibility criteria; (3) search of the literature; (4) selection of included studies; (5) extraction of results; (6) analysis; and (7) presentation of results. The presentation of results in this article was informed by the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines for scoping reviews (Shamseer et al., 2015) as recommended by Garritty et al. (2021). The purpose of the research and the research questions are outlined in the introduction above (step 1). The inclusion and exclusion criteria for the study, the search and screening strategy and the planned approach to data extraction and analysis are outlined below (steps 2–6), followed by the presentation of results (step 7).
Search Strategy
A multi-disciplinary team contributed to the development of the following search strategy for this study which is closely aligned with the research question (See Appendix for a complete description of the search strategy). The search strategy commenced with a search of academic databases for both peer-reviewed and grey literature. This was to ensure a comprehensive exploration was completed to uncover the full extent of research in this field. Furthermore, the search was limited to publications after the year 2005. This inclusion criterion was informed by the constrained skills theory (Paris, 2005) that was coined in 2005.
Sample Search Strategy
Eligibility Criteria
The following inclusion criteria were applied to the initial screening of titles and abstracts in line with the purpose and scope of the study: (i) the population of interest was children aged birth to five-years-old attending ECE services, (ii) articles were included if they reported an outcome relating to literacy skills, (iii) all study designs and reports were included; (iv) peer-reviewed articles and grey literature published in English from 2005. An assessment of methodological quality was not completed during the full-text screening of records, as the purpose of this study was to include all literature that used the terms unconstrained and/or constrained skills to describe literacy skillsets in early childhood settings. This is in line with the methodology paper by Peters et al. (2015), whereby formal assessments of methodological quality are not performed in scoping reviews.
Selection of Included Studies
A pilot exercise where 10% of the articles were screened at the abstract screening stage by all members of the research team was conducted to test and revise the eligibility criteria as necessary. This was followed by a dual screening of 20% of the records by two independent reviewers and an independent screening of the remaining records to identify texts for full-text screening (Garritty et al., 2024). Of the articles that underwent dual screening, there were conflicts between the reviewers for eight articles, mainly due to terminology differences. However, all conflicts were resolved without the involvement of a third member. Subsequently, a pilot exercise was also conducted at the full-text screening stage. The primary reviewer screened the full text of all records, and this was followed by the screening of all excluded records by a second reviewer (Garritty et al., 2024). There were no discrepancies between reviewers at this stage.
Data Extraction
The research team collectively determined which variables to extract or “chart” (Levac et al., 2010) for each included study. These included: (i) study details (including authors, year, publication type, country, and type of literature); (ii) research aims; key characteristics of literature; and (iv) key findings. Data were extracted using Covidence systematic review software.
Data Analysis
The data were synthesised to achieve the objectives of the study. The results will discuss the categories of findings related to unconstrained and constrained literacy skills in ECE research. Categories include: the benefits of ECE program attendance to child academic outcomes; evaluation of preschool programs and interventions on child academic outcomes; family involvement in supporting constrained and unconstrained literacy skills; teacher perceptions of constrained and unconstrained literacy skills; and skill development and assessment of constrained and unconstrained literacy skills.
Results
Thirty-three peer-reviewed and grey literature were included in the review. Figure 1 presents the results of the search and screening process. Flowchart of screening and selection process
Characteristics of Included Studies
Characteristics of Included Studies
Synthesis of Results
Across the 33 included articles, the terms constrained and unconstrained were used to examine the benefits of ECE programs, evaluate programs or interventions, explore teachers’ perspectives, and examine skill development and assessment. Importantly, across these areas, several studies reinformed the foundational role of constrained skills, particularly phonological awareness and letter identification, as essential early reading competencies that support later unconstrained skills.
Benefits of ECE Program Attendance to Child Academic Outcomes
Across studies, children who attended ECE programs had better outcomes in both constrained and unconstrained skills, however, the long-term sustainability of these gains varied by skill type. Constrained skills (e.g., letter-word identification) showed faster initial improvement but also the most rapid fadeout, often converging with the outcome of non-ECE attenders by the end of kindergarten and grade 1 (Ansari et al., 2020, 2023; Kholoptseva, 2016).
While Johnson et al. (2023) found a similar trend of fade out in letter-word identification and sustained vocabulary skills over kindergarten and grade 1, they also found that certain constrained skills, such as phonological awareness, which is a key predictor of early decoding, were sustained in grade 1. These findings suggest that although constrained skills often fade more quickly than unconstrained skills, they remain integral to children’s early reading development. Collectively, these studies demonstrate that distinctions between constrained and unconstrained skills help explain differential patterns of skill consolidation across the early school years but also highlight the complexity and variability in how benefits accumulate or diminish.
Evaluation of Preschool Programs and Interventions on Child Academic Outcomes
Of the 11 articles evaluating preschool programs, interventions, and curricula, a clear pattern emerged: programs tended to produce gains in the specific skill types targeted, and constrained skills typically improved when explicitly and systematically taught. As constrained skills form the building blocks for early reading acquisition, interventions focusing on phonological awareness, alphabet knowledge or letter formation typically yielded short-term gains in these foundational areas.
Two papers focused on specific interventions like rhyme training (Desmond, 2008) and Science Read-Alouds (Crouch, 2021). Desmond (2008) found that when compared to a control group, children who participated in rhyme training had higher scores in rhyme performance but not phonemic awareness. Crouch (2021) found that children in the science read-aloud groups had higher vocabulary and content knowledge scores than children in the business-as-usual group who continued to engage in the regular Pre-K curriculum.
Nine papers evaluated the content and outcomes of preschool programs and curricula, in which results were inconsistent. Programs prioritising constrained skills, such as phonological awareness and letter formation, showed improvements only in the targeted skill. Programs that focus on unconstrained skills, on the other hand, saw long-term advantages in literacy and other academic domains. Evaluations of the Early Reading First program (Hoffman, 2010) and the Get Set for School Readiness & Writing curriculum (Cypher, 2022), for example, demonstrated improvements in alphabet knowledge and letter formation, but limited or no effects on unconstrained skills, such as oral language. These findings reinforce that constrained skills, though essential for early decoding, do not generalise to broader language competencies unless intentionally supported.
In contrast, programs grounded in rich teacher-child interaction and language-focused pedagogies tended to support unconstrained skills with longer-term benefits. An evaluation of the Abecedarian (ABC) program, which emphasises high-quality, language-rich adult child interactions, found long-term gains in verbal intelligence and educational attainment (Garber, 2022), illustrating how unconstrained skills may have more durable impacts across the life course.
However, several studies showed that program and intervention impacts on both constrained and unconstrained skills often diminished over time, albeit at different speeds. An evaluation of the SPELL program in Denmark found that academic benefits gained through the intervention faded out completely by grade 2 for both constrained and unconstrained literacy skills (Bleses et al., 2021). Four papers focused on the literacy outcomes in children who attended the Boston Public School (BPS) pre-K program. McCormick et al. (2021) and Unterman (2017) found the initial benefits of BPS pre-K to diminish over time, especially for constrained skills. McCormick et al. (2022) found that the association of BPS pre-K enrolment and academic skills gained did not vary between different kindergarten instructional experiences, where the focus on constrained and unconstrained skills differs between classrooms.
That being said, the phenomenon of fade out may be due to inconsistency in the implementation of skills, including the teaching, documentation, and measurement of skills. Aust (2023) explored different teaching approaches to determine the most effective approach in supporting constrained and unconstrained skills in the classroom. Results showed that there was no consistency in the documentation or measurement of skills, especially unconstrained skills between different approaches such as Academic or Didactic Methodology, Play-Based Methodology and Play-Based with Direct Teaching approaches. Moreover, McCormick et al. (2024) highlighted that stronger fidelity in pre-K and better instructional alignment through primary school may help to sustain the initial benefits for both constrained and unconstrained skills. Across programs, the consistency and quality of implementation, and the extent to which curricula integrate both skill types, emerge as critical factors for shaping children’s long-term outcomes.
Teachers’ Perceptions of Constrained and Unconstrained Skills
Three studies focused on preschool teachers’ perceptions towards unconstrained and constrained skill development in their classrooms. Teachers reported clear guidance, structured materials and well-established pedagogical routines for teaching constrained skills, such as letter identification (Honig, 2023; McKnight-Boone, 2021; Neat, 2023). However, they described the need for a change in focus on constrained skills and limited professional support, fewer resources, and less clarity around how to intentionally development children’s oral language, comprehension and other unconstrained skills (Honig, 2023; Neat, 2023). Therefore, while teachers understand conceptually the value of both skill types, current practices and supports disproportionately favour constrained skills, limiting teachers’ capacity to support all literacy skill types.
Skill Development and Assessment of Constrained and Unconstrained Skills
Fifteen articles explored the methods and approaches to developing literacy skills in the classroom environment. Two papers explored the long-term impacts of early literacy skills on reading skills in formal school and found that greater difficulties with constrained literacy skills, such as phonological awareness in preschool, predicted greater difficulties with reading comprehension, an unconstrained literacy skill, in primary school (Cain, 2016; Murphy & Farquharson, 2016). Furthermore, five articles explored the teaching approach in preschool classrooms. Weiland et al. (2023) found that when given autonomy, preschoolers spent more time engaging in activities that promote unconstrained skills development. Findings from the other four studies suggest intentional teaching to be quality pedagogy and that teachers should consider both emotional and instructional support to meet the children’s abilities and interests (Dowling, 2016; Mantei, Kervin, & Jones, 2022; Snow & Matthews, 2016; Spring, 2019). Seven articles explored methods and approaches to support unconstrained skills like vocabulary, reading comprehension, and the writing process in the classroom (DeBruin-Parecki & Squibb, 2011; Dooley, 2011; Lennox, 2013; Mihai, 2015; Neuman & Dwyer, 2011; Rahn, 2013; Zurcher & Stefanski, 2022). Lastly, the OECD paper by Shuey and Kankaraš (2018) posited that both unconstrained and constrained skills should be evaluated to understand the foundational knowledge acquired during their early years. Overall, both constrained and unconstrained skills should be targeted in ECE, as constrained skills are necessary for the development of unconstrained skills. While children are drawn to activities promoting unconstrained skills, intentional teaching is a key component for teachers to develop children’s abilities and skills in constrained and unconstrained skills.
Discussion
The purpose of this scoping review was to examine how the terms constrained and unconstrained literacy skills are used in in early childhood education research and the extent to which researchers find these concepts useful for studying early literacy learning. While the breadth of research explicitly using these terms is limited, the review shows that the framework of constrained-unconstrained skills provides a valuable lens for understanding literacy development in ECE. Across the literature the terms were used to: (1) evaluate the benefits of ECE participation, (2) assess early literacy programs and interventions, (3) investigate teachers’ perceptions of literacy skills, and (4) examine patterns of skill development and assessment practices.
A central insight emerging from research using these terms is the different trajectories of constrained versus unconstrained skills. Key findings revealed that although both skill types fade out over time, unconstrained literacy skills are generally more sustainable than constrained literacy skills. Similar patterns of slower convergence in unconstrained skills were found across studies (Ansari et al., 2020, 2023; Kholoptseva, 2016). This trend was also evidence in evaluations of ECE programs and interventions. For example, McCormick et al. (2021) and Unterman (2017) found fadeout in academic skills, especially constrained skills, among children who attended the Boston Public School pre-K program. These findings are consistent with previous literature that found fadeout in ECE benefits on academic skills in primary school (Claessens & Garrett, 2014; Lipsey et al., 2018).
Despite the widespread prevalence of fadeout, the sustainability of literacy gains following ECE participation is not uniform. Studies showing convergence of early advantages (particularly in constrained skills) (Ansari et al., 2020, 2023; Claessens & Garrett, 2014; Kholoptseva, 2016; Lipsey et al., 2018; McCormick et al., 2021) contrast with research showing sustained benefits into primary school, high school, and even adulthood (Garber, 2022; Taggart et al., 2015; Warren & Haisken-DeNew, 2013). These divergent findings point to underlying differences in what is taught, how it is assessed, and the degree of alignment across educational settings.
Findings from this review suggest that alignment between ECE and school curricula may influence sustainability. McCormick et al. (2024) found that school-aged children who attended Boston Public School (BPS) pre-K programs showed more sustained academic growth when preschool and school curricula aligned, compared to children who experienced misalignment. Similarly, Taggart et al. (2015) suggested that changes in academic measures may explain fluctuating patterns of sustained or diminished benefits. These findings highlight the importance of alignment between early skills supported in ECE programs and those measured and reinforced in school.
Another explanation may be that the time spent developing constrained and unconstrained skills may be inconsistent across classrooms and programs, where more time spent on unconstrained skills may result in longer sustainability of academic skill benefits (Garber, 2022). Children may also gravitate toward activities that natural foster unconstrained skills (Weiland et al., 2023). However, Aust (2023) identified substantial variation in how unconstrained skills are documented and assessed across teaching approaches.
However, teachers alone cannot carry the responsibility for developing children’s unconstrained skills. While teachers are aware of instructions and approaches to teaching constrained skills (Honig, 2023; McKnight-Boone, 2021; Neat, 2023), they express the need for increased support, professional learning and resources to intentionally support children’s unconstrained skills (Honig, 2023; Neat, 2023). This underscores the broader system-level need for curriculum and program leaders to support balanced literacy promotion.
While many studies emphasise the importance of developing unconstrained skills, constrained skills remain critical as they provide the foundational competencies required for supporting the development of more complex, unconstrained skills (McCormick et al., 2021; Snow & Matthews, 2016). Evidence from several studies in this review demonstrate a reciprocal relationship between these concepts: early difficulties in constrained literacy skills, such as letter identification, phonological awareness and word reading, predict later difficulties in unconstrained literacy skills, including vocabulary and reading comprehension (Cain, 2016; Murphy & Farquharson, 2016). Conversely, once children achieve mastery in these basic reading skills, unconstrained skills, such as language comprehension increasingly drive reading comprehension abilities (Cain, 2016). This developmental progression highlights the need for balanced, intentional teaching approaches that support both skill sets to promote strong literacy trajectories.
Across the reviewed studies, a consistent theme is the need for instructional and organisational conditions that support balanced development of constrained and unconstrained skills. Teachers require not only knowledge of expected developmental progressions but also leadership support to experiment with pedagogical approaches that promote rich language and literacy learning (Honig, 2023; Neat, 2023; Snow & Matthews, 2016). Evidence also cautions against one-size-fits-all programs, which can limit teachers’ capacity to respond to children’s diverse learning needs (Mantei et al., 2021). Instead, high-quality intentional teaching that is responsive, flexible, and grounded in an understanding of both skill types appears most effective. Importantly, evaluating children’s constrained and unconstrained skills provides insight into the foundational knowledge built in the early years and is essential for supporting sustained literacy development (Shuey & Kankaraš, 2018).
Limitations and Future Research
The search strategy used in this scoping review may have limited the breadth of studies identified, as broader terms such as “language” were used, rather than more specific descriptors, e.g., “vocabulary” or “grammar”. As a result, some studies examining particular literacy skills may not have been captured. Future research would benefit from incorporating a wider range of skill-specific search terms to ensure more comprehensive coverage of the literature. In addition, as the search strategy required literature to include the terms ‘constrained’ and/or ‘unconstrained’, this requirement necessarily narrowed the pool of eligible studies and may have excluded research that investigated relevant literacy constructs without using this specific terminology. However, this was intentional as the purpose of this review was to examine how researchers define, interpret and apply these concepts.
While one non-US study examining the sustainability of ECE benefits on primary school academic outcomes revealed similar trends of fadeout (Bleses et al., 2021), research from Australia and England has found that the benefits of ECE participation can be sustained across the primary school years (Taggart et al., 2015; Warren & Haisken-DeNew, 2013). Further investigation is therefore needed to explore the development of constrained and unconstrained skills across diverse countries, cultures, and ECE contexts, and to establish whether fadeout is a global phenomenon or one that varies by system-level features. If fadeout is a phenomenon found in specific countries, future research may also provide insight into the difference in skill development and inform policies to increase the sustainability of academic outcomes.
Lastly, the focus of this scoping review was to explore the focus on constrained and unconstrained skills in early childhood. Thus, papers that explored the development and assessment of literacy skills in primary school were excluded. Given the emerging evidence of greater sustainability when skills developed in ECE programs are aligned with the teaching and assessment of skills during the formal years of schooling, it would be important for future research to explore the types of constrained and unconstrained skills focused on in primary school. Studies focusing on the alignment of skills in ECE programs to skills in primary and high school can provide insight into the relationship between the long-term alignment between school settings and the sustainability of ECE benefits on academic skills and achievement.
Conclusion
This scoping review demonstrates that although the terms constrained and unconstrained literacy skills are not yet widely used in ECE research, they offer a valuable conceptual lens for understanding children’s developmental trajectories and interpreting fadeout patterns. The review highlights a consistent trend of faster convergence in constrained skills and greater sustainability of unconstrained skills, while also identifying curriculum alignment and instructional opportunities as likely mechanisms explaining variation across contexts.
Positioning ECE practice within this framework emphasises the importance of balanced attention to both skill sets. Constrained skills may be foundational competencies, and unconstrained skills may be essential for ongoing growth in comprehension and language. The framework also underscores the need for coherent assessment practices and sustained alignment between ECE and primary school settings. Future research should therefore examine how specific constrained and unconstrained skills develop across systems and cultural contexts, and how curricular and pedagogical alignment can enhance the long-term impact of ECE programs.
This scoping review aimed to understand the concepts of constrained and unconstrained skills in early childhood education research and their relation to the profession. The review revealed that while unconstrained literacy skills are generally more sustainable than constrained skills, eventual fadeout is observed by both. This fadeout of unconstrained skills may be a result of misalignment between the development and assessment of skills across the years and a smaller emphasis on unconstrained skill development in the early years. It is important to consider the necessity of developing both constrained and unconstrained skills instead of prioritising one over the other, as the development of unconstrained skills is built upon the foundation of mastery of constrained literacy skills. This scoping review provides evidence for the current understanding of the benefits of supporting constrained and unconstrained skills in ECE programs. Future research should focus on exploring individual skills, rather than a broad category of constrained skills, to sustain long-term development of literacy, and understanding the development and appropriate assessment of constrained and unconstrained literacy skills both across grades and education systems in different countries, cultures, and contexts.
Footnotes
Ethical Considerations
Ethics approval was not required for this study, as this was a scoping review.
Consent to Participate
Informed consent was not required for this study. Participants were not involved, as this was a scoping review.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
Declaration of Conflicting Interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.