The authors examined the role of problem sets on student learning in university microeconomics. A total of 126 students participated in the study in consecutive years. independent samples t test showed that students who were not given answer keys outperformed students who were given answer keys. Multiple regression analysis showed that, along with pre-GPA and student major, a problem set with or without answer key significantly explained student learning in economics. The authors discuss the role of answer keys and implications for teaching university economics courses. (Contains 4 tables.)