Assessing students' emerging literacy skills is crucial for identifying areas where a child may be falling behind and can lead directly to an increased chance of reading success. The Waterford Assessment of Core Skills (WACS), a computerized adaptive test of early literacy for students in prekindergarten through 2nd grade, addresses this need. Initial content validity for WACS was established against state and national standards for the 11 subtests. All items were calibrated for IRT to determine item difficulty. To establish concurrent validity and predictive validity student performance on WACS was compared to performance on five commonly-used standardized tests also measuring early reading skills; all correlations between tests are highly significant. Additional analyses indicate that the test is internally coherent and has strong test-retest reliability.