Although previous research has shown that teacher coaching can improve teaching practices and student achievement, little is known about specific features of effective coaching programs. We estimate the impact of MATCH Teacher Coaching (MTC) on a range of teacher practices using a blocked randomized trial and explore how changes in the coaching model across two cohorts are related to program effects. Findings indicate large positive effects in Cohort 1 but no effects in Cohort 2. After ruling out explanations related to the research design, a set of exploratory analyses suggest that differential treatment effects may be attributable to differences in coach effectiveness, coaching dosage, and the focus of coaching across cohorts.