We evaluate the predictive validity of the Massachusetts Candidate Assessment of Performance (CAP), a practice-based assessment of teaching skills that is typically taken during a candidate's student teaching placement and is a requirement for teacher preparation program completion in Massachusetts. We find that candidates' performance on the CAP predicts their in-service summative performance evaluations the following year and provides a signal of future teacher effectiveness beyond what is already captured by the state's traditional licensure tests. Our findings add to a growing literature demonstrating that it is possible to collect information about the skills of "prospective" teachers during their teacher preparation experience that are predictive of the "in-service" outcomes of teachers.