Having highly skilled classmates appears to positively influence preschool children's academic and social development. Despite relatively consistent evidence to indicate that peers can promote positive child development, there are many issues regarding the role of peers in preschool that need to be understood in order to provide guidance to teachers and administrators who wish to capitalize on peer influence in the classroom. The goal of the present dissertation was to conduct three studies to expand current research on peer influence by reaching a more in-depth understanding of the child- and peer-level factors that contribute to the strength of peer influence in preschool. In Study One, I examined the role of child skill at entry to pre-kindergarten, in Study Two I considered child dual language learner status, and in Study Three I explored whether the relation between peer skill and child development depends on peer gender and age cohort. Study One and Two drew from a sample of 455 children who attended a state-funded prekindergarten program in rural areas of North Carolina. Study Three used data from 4,005 children attending a high-quality preschool program at 16 sites across the United States. Hierarchical linear models were used for all analyses to account for the nesting of children in classrooms. Overall, results indicated that child and peer characteristics can moderate the relation between peer skill and child development. However, the pattern of results was found to differ across the examined outcomes. Implications of these findings for the preschool classroom context are discussed. [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://www.proquest.com/en-US/products/dissertations/individuals.shtml.]