Much interest exists among parents and researchers regarding the benefits and drawbacks of delaying kindergarten entrance to acquire academic advantage ("redshirting"). How evident is this assumed advantage at the kindergarten level and beyond? The authors evaluated large-scale test data from Grades K-8 to investigate the difference in performance between younger children (summer birthday) and older children (fall birthday). The performance gap evident in kindergarten decreased rapidly in Grades 1-3 but persisted up to Grade 5, until leveling off at middle school. The performance gap in the early grades that resulted from birth date was much larger than was the gap caused by gender difference. (Contains 2 tables and 2 figures.)