Peer effects in institutions of higher education are often measured in terms of differences in student achievement after interaction with able peers. This paper uses an empirical approach to analyze peer effects on student achievement in classrooms at Colorado College. Under an ordinary least squares model, student academic rating is employed as a proxy for ability – understood to be student “quality” for the purposes of this paper – and the 4.0 GPA scale-equivalent of the grade received in a class is employed as a proxy for achievement. Specific focus is placed on the potential effects that international students and student athletes may have on the achievement of their peers. If these focus groups pose any effects, how do these effects vary with course division (humanities, natural sciences, social sciences)? This paper finds evidence of the existence of peer effects at Colorado College; specifically, international students have a large positive effect on the achievement of non-international students, and the greatest benefit from peer effects occurs in humanities courses.