Anne Prescott and Michael MitchelmoreStudent misconceptions of projectile motion in the physics classroom are well documented, but their effect on the teaching and learning of the mathematics of motion under gravity has not been investigated in the mathematics classroom. An experimental unit was designed that was intended to confront and eliminate misconceptions in senior mathematics secondary school students studying projectile motion as an application of calculus to the physical world. The approach was found to be effective, but limited by the teacher’s own misconceptions. It is also shown that teachers can reinforce student misconceptions of motion because they cannot understand why students have difficulty understanding it.