From the report: This study synthesizes existing research on the implementation of tutoring programs which we define as one-to-one or small-group instruction in which a human tutor supports students grades K-12 in an academic subject area. Tutoring has emerged as an especially promising strategy for supporting students’ academic success with strong causal evidence finding large, positive effects on students' math and reading test scores across grade levels. Prior studies have reviewed this causal evidence of effects, but none have summarized the evidence on implementation. We iteratively developed search and selection criteria to identify studies addressing key research questions and synthesized these 40 studies which employ a range of research methodologies to describe how tutoring is implemented and experienced. We find that existing research provides rich descriptions of tutoring implementation within specific programs of focus, with most studies describing after-school tutoring and small-scale programs run by university professors.