This study focused on 18 students 4-5 years old in an urban full-day preschool program in the Mid-Atlantic region of the United States. Over the course of a month, students used a touchscreen tablet to interact with Fingu, an app designed to develop students' early number sense. Using backend data generated by the app, 8,153 individual task attempts were recorded. Multilevel growth modeling, with task attempts nested within students, was used to examine the extent to which students' speed of response and response accuracy changed over the course of the study, as well as whether any individual characteristics were associated with either speed or accuracy. Results indicate that, on average, students become both faster and more accurate. Girls were also found to be more accurate than boys, and older students were found to be both slightly slower to respond and less accurate.