This paper extends research by Richard Murnane by analyzing the effects of specific teacher contract provisions on New York teacher turnover from 1972-76 and in the process assesses the validity of two theories explaining teacher mobility. The combination of the theory of human capital with the theory of internal labor markets analyzes teacher mobility in terms of the voluntary movements characteristic of the teacher shortage of the 1960's; however, a theory of institutional work rules is espoused as more useful in explaining teacher behavior during the teacher surplus of the 1970's, when job mobility tended to be involuntary. Data from a sample of 19,000 teachers from State Department of Education personnel files are subjected to logit analysis to estimate the effect of selected variables on the probability of teacher transfers and quits. Variables include a contract provision limiting class size and a provision requiring that seniority be followed in staff reductions, as well as teachers' experience levels, racial composition of teachers and of students, district enrollments, and teachers' sex. Generally, class size provisions are found to increase the probability of transfers and reduce the probability of quits, but the seniority provision affects quit rates only in districts with rapidly declining enrollment. Results are concluded to uphold the explanatory power of both theories considered. (MJL)