The purpose of this systematic literature review was to summarize outcomes of the Check-in Check-out (CICO) intervention across elementary and secondary settings. Twenty-eight studies utilizing both single subject and group (experimental and quasi-experimental) designs were included in this review. Median effect sizes across the eight group studies were small (median "d" = 0.37; range, -0.15 to 0.60) for studies reporting Cohen's "d" or similar effect sizes and large (0.23; range, 0.13 to 0.32) for studies reporting "R"[superscript 2] type effect sizes favoring the implementation of CICO. For single subject design studies, the overall median PND across 20 studies was 68% (range, 0 to 100%), indicating CICO is questionably effective but approaching the effectiveness criterion (= 70% PND) suggested by Scruggs and Mastropieri (1998). Implications for practice are discussed along with suggestions for future research.