The educational ideology of Developmentally Appropriate Practices (DAP) in childhood education is influential, despite remarkably little empirical study. This article relates DAP to changes in achievement and receptive language among former Head Start children and classmates in Grades 1-3 (including between 1,564 and 4,764 children in 869 to 1,537 classrooms). The authors applied multilevel growth curve modeling techniques to estimate overall DAP effects and to examine possible interactions with sex, ethnicity, grade, and poverty. The results were consistent across years, with only a few significant effects of DAP, some positive and others negative. Collectively, the results indicate that DAP as observed in classrooms accounts for little or no variation in children's academic performance. The article details the methodological and theoretical implications for future inquiry. (Contains 9 tables, 2 figures and 3 notes.)