To determine the effects of explicit instruction (EI) and potential moderators in second/foreign language (L2) teaching, this study meta-analyzed 28 primary reports (a total of 67 unique samples, N = 3754). The main results show that EI was significantly effective in facilitating L2 development, with effect sizes ranging from moderate to large magnitudes (d = 1.07 and 0.81 for within-and between-group contrasts, respectively). Moderator analyses show that EI type, practice type, delivery mode, length and intensity of treatment, the type of outcome measures, as well as the reporting practices of the validity and reliability of outcome measures moderated differentially the effects of EI. The findings offer important pedagogical implications for teacher-practitioners to enhance the efficacy and efficiency of EI.