The phenomenon of wheel spinning refers to students attempting to solve problems on a particular skill, but becoming stuck due to an inability to learn the skill. Past research has found that students who do not master a skill quickly tend not to master it at all. One question is why do students wheel spin? A plausible hypothesis is that students become stuck on a skill because they do not understand the necessary prerequisite knowledge, and so are unable to learn the current skill. We analyzed data from the ASSISTments system, and determined the impact of how student performance on prerequisite skills influenced ability to learn postrequisite skills. We found a strong gradient with respect to knowledge of prerequisites: students in the bottom 20% of pre-required knowledge exhibited wheel spinning behavior 50% of the time, while those in the top 20% of pre-required knowledge exhibited wheel spinning behavior only 10% of the time. This information is a statistically reliable predictor, and considering it results in a modest improvement in our ability to detect wheel spinning behaviors: R2 improves from 0.264 to 0.268, and AUC improves from 0.884 to 0.888. [For complete proceedings, see ED560503.]