Younger and older preschool-age children are commonly placed together in mixed age classrooms. However, both theory and empirical evidence conflict over whether mixed age classrooms are the best environment for developing children. A factor that may play a role in the is peer skill as children may benefit from being around more skilled peers. The present study uses a large sample of preschoolers from low income families to examine the influence of classroom age composition and peer skill on children's social and language outcomes. Using hierarchical linear analyses, results suggested that being in a mixed age classroom did not relate to the outcomes of children categorized into younger and older age groups. However, being around peers with higher language skills and fewer behavior problems tended to relate to more positive child outcomes. These findings suggest a need to support peer-to-peer contact in preschool between more and less skilled children. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]