The authors examined the impact of a supplemental reading course on 462 sixth-grade students' reading engagement and performance as compared with 389 students in a control group. They further explored students' cognitive strategy use through think aloud processes with a subset of students who participated in the intervention. Participating students reported significantly higher levels of strategy use, intrinsic motivation, extrinsic motivation, and self-efficacy as compared with the control group. Think aloud measures indicated students who participated in supplemental instruction exhibited higher levels of cognitive engagement at the end of the intervention than they exhibited at the start of the intervention. There was no significant impact on students' reading performance as measured by a standardized test.