There are currently 2 principal models of publicly funded prekindergarten programs (pre-K): targeted pre-K, which is means-tested, and universal pre-K. These programs often differ in terms of the economic characteristics of the preschoolers enrolled. Studies have documented links between individual achievement in school-age children and the economic composition of classroom peers, but little research has revealed whether these associations hold in pre-K classrooms. Using data from 2,966 children in 709 pre-K classrooms, we examined whether classroom-economic composition (i.e., average family income, standard deviation of incomes, and percentage of students from low-income households) relates to achievement in preschool. Furthermore, this study investigated whether associations between classroom-economic composition and achievement differed depending on initial academic skill level. Increased economic advantage in pre-K classrooms positively predicted spring achievement. Specifically, increasing aggregate classroom income between $22,500 and $62,500 was related to improvements in math scores. Increases in the proportion of children from low-income households in the classroom were negatively related to both math and literacy and language skills when increases occurred between 52.5% and 72.5% and 25% and 45%, respectively. There was limited evidence that links between classroom-economic composition and achievement differed depending on initial skill level. Results suggest that economically integrated pre-K programs may be more beneficial to preschoolers from low-income households' achievement than classrooms targeting economically disadvantaged children. (author abstract)