A study is described that tested the effectiveness of computer-assisted tutorial modules in dispelling common student misconceptions in first-year mechanics. Most of the subject matter for the tutorial modules was based on examples drawn from kinematics and dynamics, which one would find on many first-year physics tests. One of the examples, involving qualitative comparison of speeds of two differently moving objects, has been the subject of investigations of student misconceptions conducted by other workers. The present study involved a total of 96 student volunteers drawn from all of our first-year physics courses. The results of the study suggest that computer-assisted tutorials of the kind described here can be effective in teaching material that presents conceptual difficulties, and is often not learned directly from textbooks or from lectures delivered to large classes.