The Letter-Sound Short Forms (LSSFs) were designed to meet criteria for effective progress monitoring tools by exhibiting strong psychometrics, offering multiple equivalent forms, and being brief and easy to administer and score. The present study expands available psychometric information for the LSSFs by providing an initial examination of their validity in assessing young children's emerging letter-sound knowledge. In a sample of 998 preschool-aged children, the LSSFs were sensitive to change over time, showed strong concurrent validity with established letter-sound knowledge and related emergent literacy measures, and demonstrated predictive validity with emergent literacy measures. The LSSFs also predicted kindergarten readiness scores available for a subsample of children. These findings have implications for using the LSSFs to monitor children's alphabet knowledge acquisition and to support differentiated early alphabet instruction.