Background. Handwriting difficulties are among the most common reasons for referral of children to occupational therapy. Purpose. To determine the effectiveness of handwriting interventions. Methods. A systematic review was carried out. Included studies were randomized or nonrandomized controlled trials of interventions that could be used by an occupational therapist to improve written output (printing or writing) among school-aged children identified as having difficulties with handwriting. Electronic searches of relevant databases were conducted up to January 2010. Findings. Eleven studies met the inclusion criteria. These studies tested (1) relaxation and practice with or without EMG, (2) sensory-based training without handwriting practice, and (3) handwriting-based practice (including sensory-focused or cognitive focused handwriting practice). Regardless of treatment type, interventions that did not include handwriting practice and those that included less than 20 practice sessions were ineffective. Implications. Effective occupational therapy for improving handwriting must include adequate handwriting practice.