This study extends previous work conducted with a sample of primarily low-income children attending an enhanced, publicly funded preschool program and assesses the effect of preschool dosage (i.e., receiving one or two years of preschool) on children's academic and executive function (EF) outcomes at first and second grade. Because random assignment of children to receive one or two years of preschool was not possible, we used propensity score one-to-one matching to create two groups of equal size--a one-year group (i.e., those who attended preschool for one year and represented low preschool dosage, N = 144) and a two-year group (i.e., those who attended preschool for two years and represented high preschool dosage, N = 144) to control for potential selection bias. With respect to academic skills, children in the two-year group had higher scores on receptive vocabulary (as assessed by the Peabody Picture Vocabulary Test, Third Edition) and math skills (as assessed by the Applied Problems subtest of the Woodcock-Johnson Psychoeducational Test Battery-Revised [WJ-R]). They also had higher Broad Reading composite scores on the WJ-R at second grade. With respect to EF skills, at both first and second grade, children in the two-year group had higher scores on a working memory task (Backward Digit Span); they also made fewer perseverative errors and completed more categories on a task assessing set-shifting (Wisconsin Card Sort Task-64). Finally, children in the two-year group were better adjusted in school (i.e., they were less likely to have been retained or have received special education services by second grade). Effect sizes ranged from 0.22 to 0.40, suggesting that providing low-income children with an extra year of high-quality preschool continues to benefit students into elementary school. We discuss implications of the findings for public policy. (author abstract)