We evaluated the utility of a brief, seven‐item, teacher‐rated Peer Social Maturity Scale (PSMAT). In Study 1, teachers of 138 Australian children (ranging from 5 to 8 years and 5 months old) in kindergarten and Grades 1 and 2 rated their pupils' social maturity using the PSMAT and their classroom social skills via the Social Skills Rating System (SSRS). The PSMAT showed excellent internal consistency and a significant overall correlation with the SSRS social skills scale. Study 2 involved a new longitudinal sample of children who were rated by different classroom teachers in kindergarten and Grades 1 and 2 of full‐time primary school. Consistent with Study 1, at all three time points, PSMAT scores were highly correlated with SSRS social skills scores. PSMAT scores also correlated significantly with peer‐rated social preference. These studies confirm that the PSMAT is a reliable and valid assessment of children's social maturity within their classroom peer groups. Copyright © 2013 John Wiley & Sons, Ltd.