This meta-analysis synthesized recent research on strategy instruction (SI) effectiveness to estimate SI effects and their moderators for two domains: second/foreign language and self-regulated learning. A total of 37 studies (47 independent samples) for language domain and 16 studies (17 independent samples) for self-regulated learning domain contributed effect sizes for this meta-analysis. Findings indicate that the overall effects of SI were large, 0.78 and 0.87, for language and self-regulated learning, respectively. A number of context (e.g., educational level, script differences), treatment (e.g., delivery agent), and methodology (e.g., pretest) characteristics were found to moderate SI effectiveness. Notably, the moderating effects varied by language versus self-regulated learning domains. The overall results identify SI as a viable instructional tool for second/foreign language classrooms, highlight more effective SI design features, and suggest a need for a greater emphasis on self-regulated learning in SI interventions and research.