Research Findings-Data on more than 900 children participating in the National Institute of Child Health and Human Development Study of Early Child Care were analyzed to examine the effect of age of entry to kindergarten on children's functioning in early elementary school. Children's academic achievement and socioemotional development were measured repeatedly from the age of 54 months through 3rd grade. With family background factors and experience in child care in the first 54 months of life controlled, hierarchical linear modeling (growth curve) analysis revealed that children who entered kindergarten at younger ages had higher (estimated) scores in kindergarten on the Woodcock-Johnson (W-J) Letter-Word Recognition subtest but received lower ratings from kindergarten teachers on Language and Literacy and Mathematical Thinking scales. Furthermore, children who entered kindergarten at older ages evinced greater increases over time on 4 W-J subtests (i.e., Letter-Word Recognition, Applied Problems, Memory for Sentences, Picture Vocabulary) and outperformed children who started kindergarten at younger ages on 2 W-J subtests in 3rd grade (i.e., Applied Problems, Picture Vocabulary). Age of entry proved unrelated to socioemotional functioning.Practice-The fact that age-of-entry effects were small in magnitude and dwarfed by other aspects of children's family and child care experiences suggests that age at starting school should not be regarded as a major determinant of children's school achievement, but that it may merit consideration in context with other probably more important factors (e.g., child's behavior and abilities).Perhaps no other issue appears so frequently and dominantly in parents' discussions of school readiness or school districts' readiness policies as that of the age at which children are eligible (or required) to start kindergarten. When parents are surveyed about their children's school readiness and enrollment, one of the most frequent questions noted is whether their child is too young to enroll (e.g., West, Hauske, & Collins, 1993). Kindergarten teachers identify age as a factor that figures prominently in definitions and beliefs about readiness for kindergarten, and age is often used as a post hoc explanation for decisions to retain children in kindergarten (National Center for Education Statistics [NCES], 1993a).Age of entry to school is also of considerable policy importance (Meisels, 1992(Meisels, ,1999. It is an index society uses as an eligibility or selection mechanism for access to public resources and, consequently, an index that triggers potential benefits of stimulation gained by attendance in school. Given that, within a 12-month year, older children tend to show more advanced developmental skills than younger children, changes in age of entry can have effects on the percentages of children who meet certain academic or skill standards and can boost a district's standing on certain metrics (Vecchiotti, 2001). In short, age of entry to school figures prominently in teacher ...