A Meta-Analysis of Single-Subject-Design Intervention Research for Students with LD

This article summarizes single-subject-design intervention studies that include students with learning disabilities. Effect sizes of 85 studies were analyzed across instructional domains (e.g., reading, mathematics); sample characteristics (e.g., age, intelligence); intervention parameters (e.g., number of instructional sessions, instructional components); and methodological procedures (e.g., internal validity, treatment integrity, sample representation). The major findings were as follows: (a) All domain areas except handwriting yielded effect sizes at or above Cohen's .80 threshold for a substantial finding; (b) instructional components related to drill-repetition-practice-review, segmentation, small interactive groups, and the implementation of cues to use strategies contributed significant variance (15%) to estimates of effect size; (c) strategy instruction (SI) models better predicted effect size estimates than direct instruction (DI) models when the results were qualified by the reported intellectual and reading levels of the participants; (d) high-IQ discrepancy groups yielded lower effect sizes compared to low-IQ discrepancy groups in the domain of reading, whereas the reverse effect occurred when treatment outcomes were not reading measures; and (e) the low-IQ discrepancy groups yielded higher effect sizes for a Combined DI and SI Model when compared to competing models. The results are supportive of the pervasive influence of cognitive strategy and direct instruction models across treatment domains and of the notion that variations in sample definition moderate treatment outcomes.