During the past 25 years, a steadily increasing fraction of children has entered kindergarten after their sixth birthday instead of the more traditional route of beginning at age five. Part of this increase has been due to changes in state education laws that require children to be born earlier in the calendar year to be eligible to begin kindergarten each fall, but some of the increase resulted from choices by parents to voluntarily delay their child's entry into kindergarten by a year, hoping to improve their child's "kindergarten readiness". This project studies the causes and consequences of delayed kindergarten enrollment. We use several large, nationally representative data sources to study four specific questions: (1) What is the effect of state entrance-age laws on children's reading and math skills, grade progression, and probability of being diagnosed with either a learning disability or Attention Deficit Hyperactivity Disorder? (2) What is the effect on these outcomes of parents voluntarily delaying their child's entry into kindergarten? (3) Are the effects of delayed entry different for children from high- and low-socioeconomic status families, and if so, why? (4) Do the impacts of delayed entry primarily stem from a child's absolute age at entry, or her age relative to her peers? We address these questions using several statistical approaches, including instrumental variables models and propensity score matching. These techniques allow us to explore whether some children benefit from delayed enrollment more than others. For example, children with health problems may be particularly good candidates for delayed enrollment, especially if there is a good chance that the child's health may improve in the intervening year. By contrast, there may be a very limited benefit to delayed enrollment among poor children with little access to pre-school or other programs that will promote cognitive or psychological growth. Policymakers, educators, and parents have increasingly encouraged delayed enrollment as a method to improve the educational experience and outcomes of children, especially poor children and those at risk of falling behind later in their academic careers. Our research better informs the national discussion on these issues. [unreadable] [unreadable] [unreadable]