The study described in this paper investigates the combined effect of certain variables on student achievement in classical mechanics. Our purposes are (1) to describe the preinstructional knowledge of mechanics, mathematical skills, and reasoning skills of a sample of college physics students, (2) to correlate these variables with the student’s success in learning classical mechanics, and (3) to develop an hypothesis about the relationships between these variables and student achievement in mechanics. We also offer some proposals for improving the teaching of classical mechanics.