Successful preschool transition is important for future educational success. We used brief functional screenings to identify low-income children at risk for difficulty transitioning into preschool. Functional screenings were conducted for 163 children prior to enrollment, in a naturalistic peer setting, and focused on multiple domains important for successful classroom transition, including social and emotional skills as well as cognitive and language abilities. Children were assigned a transition risk rating based on strengths and/or concerns in language, cognition, externalizing/internalizing, social skills, and affective tone. Social and emotional classroom behaviors were primary outcomes of interest due to the importance of early socio-emotional competence for later adjustment. Outcomes were assessed using multiple methods and multiple informants, including live classroom observations. The brief functional screening predicted outcomes almost one year later. Findings are discussed regarding implications for incorporating a whole-child, functional approach to existing screening practices, and applying developmental research methods to prevention science. (Contains 4 tables.)