Early number skills are a critical aspect of early mathematics development. However, the constructs that comprise early number skills differ across assessments, and previous studies have proposed various models of early mathematics skills comprised of formal and informal tasks. This study explored the factor structure of a researcher-developed measure of mathematics administered to a large, geographically diverse sample of kindergarten students at risk for mathematics difficulty (n = 580) in a randomized control trial. Consistent with previous research, factors representing early number skills and task types emerged. Importantly though, the best fitting model was one in which both skill types (e.g., number identification, magnitude comparison) and task types (i.e., informal and formal) were modeled. The inclusion of task type as a factor in early mathematics assessment has many potentially important ramifications. Recommendations for attending to task types when assessing early number skills, and implications for instruction and measurement are discussed.