Grouping by Achievement: The Importance of Ordinal Rank and Tutors’ Instructional Practices Evidence from a Large Norwegian Field Experiment

We use data from a Norwegian field experiment where young students were taught mathematics in small, homogenous groups to investigate how treatment effects varied across middle-achieving students dependent on their rank order and their tutors’ instructional practices. We find that individuals from the second and fourth quintiles in the pretest score distribution who were placed in groups with lower (higher) ranked students experienced substantially lower (higher) treatment effects than students who were placed in groups with students from the same quintile as themselves. These effects were somewhat modified by the tutors’ instructional practices. Students in the third quintile were unaffected by their within-group rank.