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α: calibrated so average coauthorship-adjusted count equals average raw count
We analyse peer effects among students of a middle-sized Italian public university. We explain students' average grade in exams passed during their Second Level Degree course on the basis of their pre-determined measures of abilities, personal characteristics and peer group abilities. Thanks to a rich administrative data set, we are able to build a variety of definitions of peer groups, describing different kinds of students' interaction, based on classes attended together or exams taken in the same session. Self-selection problems are handled through Two-Stage Least Squares estimations using as an instrument, the exogenous assignment of students to different teaching classes in the compulsory courses attended during their First Level Degree course. We find statistically significant positive peer group effects, which are robust to the different definitions of peer group and to different measures of abilities.