We investigate patterns of teacher mobility in districts with different collective bargaining agreement (CBA) transfer provisions. We use detailed teacher-level longitudinal data from Washington State to estimate the probability that teachers of varying experience and effectiveness levels transfer out of their schools to another school in the district, to another district, or out of Washington K-12 public schools. We find consistent evidence that within-district transfer probabilities increase with the proportion of disadvantaged students in a school for veteran teachers but decrease with the proportion of disadvantaged students for novice teachers, and that the strength of these relationships is associated with the strength of seniority transfer provisions in CBAs. Specifically, the pattern of veteran teachers leaving disadvantaged schools and novice teachers staying in disadvantaged schools is more pronounced in districts with strong CBA seniority transfer protections. CBA transfer provisions do not, however, appear to be an important factor in teacher transfers out of school districts or the K-12 public school workforce in Washington. Finally, we find some evidence that more effective teachers are more likely to stay in advantaged schools when seniority is not a factor in transfer decisions. A bibliography is included.