Self-selecting peer groups formed within the laboratory environment have a lasting effect on individual student attainment and working practices.

Within the present study, we investigate the lasting effect of laboratory peer group interactions on the end of year attainment of Biosciences and Chemistry students. By asking students to identify who they primarily work with within the laboratory environment and evaluating the interactions through cluster analysis, we identified two main categories of laboratory peer groups: the first long-lived well-established pairings of two students, 'swans', who work together for all or the majority of the laboratory sessions; and the second dynamic fluid groups, 'dolphins', of between three and nine students who work with each other interchangeably. Statistical analysis is presented, which demonstrates that individuals within each laboratory peer group were likely to achieve a similar average mark at the end of the first year of study on the course. We identified the driving factors for the formation of these groups as friendship and perceived work ethic. There is a preference for high-achieving students to work with other high-achieving students and lower-achieving to group around a shared social background. Targeted interventions, in which pairings were selected by the tutor at the onset of the study, altered the ratio from long-lived pairs to more dynamic groups and increased students' willingness to work with others outside of their group but did not change the drivers of group formation or resulting pattern of achievement. We conclude with recommendations around group working within the laboratory environment.