Evidence suggests that compensation affects teacher retention. In general, studies have concluded that higher teacher pay increases the likelihood that a person will continue to teach. Similarly, attractive earnings opportunities outside teaching encourage people to leave the teaching profession. While these findings are intuitive, researchers have used a variety of approaches when measuring compensation, and only a few include measures of expected future earnings. This paper makes use of the Annualized Cost of Leaving (ACOL) model, a framework developed by military manpower analysts, to estimate the effect of current and future relative earnings on teacher retention. While the ACOL model is used and widely accepted by all branches of the military to analyze manpower issues, it has been used in only a few applications outside the military. The authors assert, that to their knowledge, this paper is the first to apply it to an analysis of teacher retention, and the first to model the effect of teachers' future earnings opportunities in a theoretically defensible fashion.