Evidence that student learning declines or stagnates during summers has motivated an interest in programs providing intensive summer instruction. However, existing literature suggests that such programs have modest effects on achievement and no impact on measures of engagement in school. In this quasi-experimental study, we present evidence on the impact of a comprehensive and mature summer learning program that serves low-income middle school students and features unusual academic breadth, including a robust and well-designed social-emotional learning curriculum. 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 are dynamic, growing over time and with additional summers of participation.