Modern economics courses require high mathematical proficiency, and low proficiency may reduce grades or cause students to avoid economics courses. The article's authors sought to improve students' mathematical skills and grades with a simple intervention based on repeated quizzing of building-block concepts. They analyzed data from four semesters of a first-year course. During the first two semesters, there were five online quizzes, and each concept appeared on only one quiz. During the latter two semesters, important basic concepts appeared repeatedly across quizzes. Performance with repeated concepts improved across quizzes, and repeated quizzing was associated with slightly higher final exam scores. Mid-semester exam scores, which preceded most quizzes, were not consistently associated with the quizzing approach, helping to rule out cohort effects and other alternative explanations.