Separating students into homogeneous groups is a common instructional practice used by elementary teachers during reading instruction. Although researchers have been studying the effects of homogeneous grouping for many decades, there is little consensus on whether grouping is an effective or equitable instructional practice. The central challenge in estimating the effects of grouping is determining an appropriate comparison case for homogeneously grouped students. Using data from the 2010 cohort of the Early Childhood Longitudinal Study, this study uses student fixed effects to compare the reading growth of students who have different grouping experiences during reading instruction over their first 3 years of schooling. This study finds that, on average, homogeneously grouped students have slightly higher reading growth than students who are not grouped but also finds that this association between homogeneous grouping and reading growth depends on students' reading group placement and initial reading skills.