One of the most consistent findings in the literature on teacher quality is that teachers improve with experience, especially in the first several years. This study extends this research by separately identifying the benefits of general teaching experience and specific curriculum familiarity. I find that both specific and general human capital contribute to teacher improvement and that recent specific experience is more valuable than distant specific experience. This paper also contributes to a broader literature on human capital acquisition, as it is among the first to examine human capital specificity using a direct measure of productivity. (JEL H75, I21, J24, J45)