The purpose of this study was to conduct a descriptive and quantitative review of the literature examining the effectiveness of check-in check-out (CICO), a commonly used behavioral intervention in the context of a Positive Behavior Interventions and Supports framework. Studies that experimentally investigated the effectiveness of CICO or modified CICO compared with a baseline or control condition on student outcomes were included. A between-case "d"-statistic comparable across single-case and between-groups experiments was calculated for 59 dependent variables across 32 studies. The meta-analysis was conducted using robust variance estimation allowing for the inclusion of multiple effect sizes per study by accounting for dependency between outcomes. The overall effect size, g-bar = 1.22, 95% confidence intervals (1.00, 1.44), suggested CICO improves student outcomes by over one standard deviation. Studies were characterized by considerable heterogeneity that went largely unexplained in moderator analyses. Results are situated in the context of other systematic reviews of CICO and modified CICO. Overall, CICO appears to be an effective intervention; however, at this time, it is unclear what study- and sample-level variables may impact its effectiveness.