The social and behavioral ecology of mixed-age and same-age preschool classrooms: A natural experiment Adam Winsler a, *, Sarah L. Caverly a , Angela Willson-Quayle a , Martha P. Carlton b , Christina Howell c , Grace N. Long d a Department of Psychology, George Mason University, 3F5 4400 University Drive, Fairfax, VA 22030-4444, USA b Southern Illinois University, Edwardsville, IL, USA c California State University, Bakersfield, CA, USA d University of Alabama, Tuscaloosa, AL, USA Abstract Social interaction and task behavior of preschool children in mixed-age (MA) and same-age (SA) groups were studied longitudinally in this natural experiment, which capitalized on one preschool’s transition from two SA (separate 3, 4) classrooms to two MA (combined 3/4) classrooms. In contrast to previous research examining MA and SA grouping, which has typically lacked appropriate comparison groups, the present study was essentially able to hold teachers, curriculum, location, teaching philosophy, and participant population constant. A total of 7887 naturalistic, time-sampled, classroom observations on 47 children attending the two classes were conducted over the course of 18 months. Children’s goal-directed activity, sustained attention, social affiliation, inappropriate behavior, and affect were reliably recorded using a checklist instrument. Significant age differences in behavior between the 3- and 4-year-olds in SA classrooms were typically eliminated in the context of MA classrooms such that the 3-year-olds in MA classes in several ways were more like 4-year-olds in SA classrooms, and 4-year-olds in MA classes behaved more like 3-year-olds in SA classrooms. The social and behavioral ecology of the MA preschool classrooms changed significantly over time as children became more familiar with one another. Several of the social affiliation advantages of MA grouping that were found (i.e., age and gender desegregation) wore off over time as the school year progressed. The effects of MA grouping on children’s social and behavioral development appear complicated. Developmental 0193-3973/02/$ – see front matter D 2002 Elsevier Science Inc. All rights reserved. PII:S0193-3973(02)00111-9 * Corresponding author. Tel.: +1-703-993-1881; fax: +1-703-993-1359. E-mail address: awinsler@gmu.edu (A. Winsler). Applied Developmental Psychology 23 (2002) 305 – 330