The authors evaluated the effectiveness of explicit reading comprehension strategies instruction, followed by practice in teacher-led whole-class activities (STRAT), reciprocal same-age (STRAT + SA) peer-tutoring activities, or cross-age peer-tutoring activities (STRAT + CA) on 2nd and 5th graders' reading comprehension and self-efficacy perceptions. For 2nd graders, multilevel analyses revealed significant STRAT and STRAT + CA effects; however, the effects did not last after finishing the program. Fifth graders in all 3 experimental conditions performed significantly better on the posttest than their control group peers. Results also showed continued growth for the STRAT and STRAT + CA conditions until at least 6 months after students finished the program. Moreover, on both the posttest and retention test, 5th graders in the STRAT + CA condition reported significantly fewer negative thoughts related to their reading proficiency.