We describe a program that provides structured practice of prerequisite material to students in an ordinary differential equations course using an existing automated homework system originally designed for precalculus and calculus classes. The goal of the program is to improve students' comprehension of material presented in class by timing the review to occur just before the prerequisite material is relevant in class. The review is designed to gain class time that would otherwise be dedicated to review, with minimal involvement of the instructor. We report positive responses from both instructors and students in two sections of the course. (Contains 5 figures and 1 footnote.)