We study the impact of peer effects on the academic achievement of economics students in Pontifical Catholic University of Ecuador (PUCE) Ecuador, for both semesters of 2018. The estimates from our random-effects model show a significant influence of the average-group, high-achieving, and low-achieving peers. These results are robust with the presence of socioeconomic, academic, and teaching quality covariates. The findings suggest that systems that prioritize course enrollment according to previous scores may exacerbate a peer-driven bias in student performance.