Multigrade teaching and age composition of the class: The influence on academic and social outcomes among students

•We looked at the effects of the age composition of the class on student outcomes.•We used Growing Up in Ireland data on nine-year-old children.•We found few overall differences between single-grade and multigrade classes, all else being equal.•However, girls had lower achievement and more behavioural problems in classes with older peers.•Girls were more negative about their academic performance and popularity when taught with older or younger peers.

This article presents innovative analyses on the effects of the age composition of the class using the first wave of a large-scale longitudinal study of nine year old children, the Growing Up in Ireland study. The analyses focus on both academic and social outcomes. Taking account of a rich set of control factors, few overall differences were found in student outcomes between single-grade and multigrade classes. However, girls were found to experience a range of negative effects, depending on the age composition of the class.