This paper analyzes the relationship between leadership, teacher collaboration, and student achievement in elementary schools. Across 96 elementary schools, this study included treatment and control schools, drawing on 1,600 surveys conducted with teachers. The authors highlighted three important findings. First, schools where principals engaged in shared instructional leadership increased rates of teacher collaboration. School leaders are instrumental in fostering an environment where teachers work together to make pedagogical improvements. Second, the study showed that student achievement increased when teachers engaged in collaborative work toward instructional improvements. Specifically, a strong relationship was found between teacher engagement in collaboration and third graders’ achievement in math and reading. Third, this study indicated an indirect but instrumental relationship between shared instructional leadership and student achievement. When principals actively engage in instructional activities, it creates support systems between teachers to work toward instructional and pedagogical improvements. While not focused on MLs, this article highlights the nested relationship between leadership on teacher collaboration and its effect on student achievement.