The evidence that student learning declines sharply (or stagnates) during the summer has motivated a substantial interest in programs that provide intensive academic instruction during the summer. However, the existing literature suggests that such programs, which typically focus on just one or two subjects, have modest effects on students' achievement and no impact on measures of their engagement in school. In this quasi-experimental study, we present evidence on the educational impact of a unique and mature summer learning program that serves low-income middle school students and features unusual academic breadth and a social emotional curriculum with year-to-year scaffolding. Our results indicate that this program led to substantial reductions in unexcused absences, chronic absenteeism and suspensions and a modest gain in ELA test scores. We find evidence that the gains in behavioral engagement grow over time and with additional summers of participation. Our results also suggest that these effects were particularly concentrated among boys and Latinx students. [This work was funded by a grant to The John W. Gardner Center for Youth and their Communities (Gardner Center) by Aim High.]