Performance of 5000 students in introductory mechanics*

We present the performance of nearly 5000 students on a standardized assessment of force and motion (Force Concept Inventory) for two fundamentally different physics curricula; a traditional course based on the Knight text and a reform course based on the text of Chabay and Sherwood, Matter and Interactions (M\&I). The traditional course is a standard physics curriculum with particular emphasis on constant force motion. The M\&I course is a modern approach to physics instruction with computer modeling and an emphasis on the generality and dynamics of Newton's Second Law. We find poorer performance for students who have taken the M\&I course as compared to students taking the standard course. This under-performance is consistent despite the superior performance by M\&I students on common exam problems in other areas of mechanics. We offer explanations for this consistent under-performance in the realm of force and motion as well as some results from recent work to combat these misconceptions in the M\&I course.