Engagement and academic achievement are generally correlated among elementary school students without learning disabilities (LDs). However, it is unclear if this pattern holds for students with LDs, who have lower achievement and engagement than their peers. This study examined whether links between achievement and student-reported behavioral engagement operate differentially for students with and without LDs in a nationally representative U.S. sample (N [approximately equal] 15,660). Multiple group path analyses demonstrated that associations between third- and fourth-grade achievement were stronger for students with LDs, compared with students without LDs. For children without LDs, engagement mediated all pathways from third-grade to fourth-grade achievement. For students with LDs, engagement only mediated the pathway from third-grade math to fourth-grade reading. Overall, our study emphasizes the crucial role of early achievement for later school success, particularly for students with LDs. We discuss the importance of early intervention to support LD students' academic achievement and engagement. [This paper will be published in the "Learning Disability Quarterly."]