We utilize detailed teacher-level longitudinal data from Washington State to investigate patterns of teacher mobility in districts with different collective bargaining agreement (CBA) transfer provisions. Specifically, we estimate the log odds that teachers of varying experience and effectiveness levels transfer out of their schools to other schools in the district in Washington kindergarten through 12th grade (K-12) public schools. We find little consistent evidence relating voluntary transfer provisions in CBAs to patterns in teacher mobility, but do find evidence that patterns in within-district mobility by teacher experience and effectiveness vary between districts that do not use seniority in involuntary transfer decisions and those that use seniority as a tiebreaker or the only factor in these moves. In models that consider teacher experience, the interaction between teacher experience and school disadvantage in teacher transfer decisions is more extreme in districts with strong involuntary seniority transfer protections; novice teachers are even more likely to stay in disadvantaged schools, and veteran teachers are even more likely to leave disadvantaged schools. On the other hand, models that consider value-added measures of teacher effectiveness suggest that more effective teachers are less likely to leave disadvantaged schools in districts that do use seniority in involuntary transfer decisions, that is, seniority transfer provisions could actually make the distribution of output-based measures of quality more equitable. Taken together, these results suggest that seniority transfer provisions may have differential impacts on the distributions of teacher experience and effectiveness.