Policy implementation research indicates that local contexts and school factors shape how teacher collaboration efforts are implemented in schools. By evaluating a statewide teacher collaboration initiative in Tennessee known as the Instructional Partnership Initiative (IPI), this article provides insight on the school level factors that are associated with participating teachers' frequency of IPI collaboration activities and a collaborative focus on instructional practices. We estimate a series of regression models and find that school supports and characteristics of teacher partnerships were significant predictors of the frequency of collaborative activities, focus on instructional activities, and perceptions of IPI as beneficial. Commonalities among partner teachers like subject/grade taught were also associated with teachers' perceptions of IPI as beneficial. Our results contribute to the broader understanding of how schools can encourage teacher engagement in collaborations that focus on instructional improvement. [This article was published in "American Journal of Education" (EJ1307998).]