The aim of this study was to investigate the effectiveness of a formative assessment system in improving students’ learning. This system involved giving feedback to students regarding the errors they made in a series of assignments performed during a course. Participants were 166 students enrolled in a core course of the degree in psychology offered by the University of Barcelona. Attendance at feedback classes was found to be positively correlated with students’ grades, whereas the correlation between math anxiety scores and final exam grades was not significant. Exam grades were only predicted by the ‘perceived usefulness of feedback’ factor, suggesting that feedback may have helped to reduce the negative impact of math anxiety on students’ academic achievement.