There is growing consensus about the importance of teacher collaboration. Less clear are the mechanisms by which teacher collaboration can positively impact student achievement. We address this gap by examining two questions using panel data methods. First, does the degree to which teachers collaborate predict future growth in conditions relevant to student learning, including teachers' instructional practice, instructional climate, and trust relations? Second, does growth over time in collaboration affect growth in these outcomes? We find evidence that both collaboration at baseline and its growth over time are positive predictors of change in teacher practice, instructional climate, and trust relations.