As educational policy makers seek strategies to improve the teacher workforce, the early career period represents a unique opportunity to identify struggling teachers, examine the likelihood of future improvement, and make strategic pretenure investments in development or dismissals. It is also a useful time to identify particularly promising teachers for development and focus on high-needs areas. This article asks how much teachers vary in performance improvement during their first 5 years of teaching and to what extent initial job performance predicts later performance. We find that, on average, initial performance is quite predictive of future performance, far more so than typically measured teacher characteristics. This is particularly the case in math, while predictions about future English language arts (ELA) performance based on initial ELA value added are less precise. Predictions are most powerful at the extremes. We use these predictions to explore the likelihood that personnel actions based on initial performance would lead to inappropriate distinctions between teachers who would be high or low performing in future years. We also examine the much less discussed costs of failure to distinguish performance when meaningful differences exist. The results point to the potential of policies that make use of teachers’ initial performance to inform personnel decisions.