This paper examines the effect of a weekly student self-assessment assignment on student performance in an undergraduate math course. Self-assessment is an increasingly popular type of formative assessment with close ties to self-regulated learning theory. In this randomized controlled trial, 88 students enrolled in MAT 142 were divided into four treatment groups, receiving the self-assessment assignment for either half the semester, the full semester, or not at all. There was no main effect of the treatment on students’ course performance (F(3,80) = 0.154, p = 0.999). However, students’ level of compliance with the assignments (F(1, 63) = 6.87, p = 0.011) and class attendance (F(1, 83) = 12.34, p < 0.001) both significantly predicted exam scores, suggesting that conscientiousness predicts performance. I conducted focus groups to understand how students felt toward the self-assessments. Participants expressed distaste toward the assignments and provided suggestions for improvements. I describe these improvements, among others, in an effort to outline future directions for this research. I also describe a new model of student self-assessment based on theories of adaptive testing and self-regulated learning.