The purpose of this paper was to test the relationship between principal leadership and teacher collaboration around instructional improvement to determine whether these measures were statistically related and whether, together, they were associated with academic achievement in elementary schools. Data were obtained from 1,600 teachers in 96 elementary schools where principals are participating in a randomized control trial to assess the efficacy of a widely-disseminated professional development program for school leaders. Using structural equation modeling, we found a significant direct effect of leadership on teacher collaboration and a significant direct effect of collaboration on student achievement. Also, the indirect effect of leadership on student achievement through teacher collaboration was significant. These findings have implications for practitioners and researchers. An appendix provides: Shard Instructional Leadership and Collaboration Factor Scale Measurement Properties. (Contains 7 tables and 2 figures.) [The research reported here was conducted by the Education Leadership Research Center (ELRC) at Texas A&M University as part of the School Leadership Improvement Study (SLIS).]