Of the myriad practices currently utilized for students with disabilities, particularly students with or at risk for emotional and/or behavioral disorder (EBD), functional behavior assessment (FBA) is a practice with an emerging solid research base. However, the FBA research base relies on single-subject design (SSD) and synthesis has relied on literature review or analyses using nonparametric effect size calculations. This study was designed to examine the omnibus effect that FBA-based interventions have on problem behaviors for students with or at risk for EBD in schools using a hierarchical linear modeling meta-analytic approach to SSD synthesis. Based on a sample of 69 FBA studies, 146 subjects, and 206 outcome graphs, results indicated that, overall, FBA-based interventions reduced problem behavior by an average of 70.5% and that the procedure was effective across all student characteristics. Differences of effectiveness were evident between functional analysis and descriptive assessment procedures. Findings of this study suggest that FBA based interventions for students with or at risk for EBD are an effective approach for the reduction of problem behaviors. (Contains 5 tables and 1 note.)