Selective sustained attention (SSA) is an important cognitive process enabling everyday functioning and task performance by allowing us to: 1) choose components of our environment to process at the exclusion of others and 2) maintain focus on those components over time. Although SSA is known to undergo rapid and marked changes during the preschool and early primary school children years, there has been little behavioral data on these years due to a lack of child-appropriate testing paradigms. The TrackIt paradigm was recently developed to fill the previously existing measurement gap for SSA in these years. We analyzed errors that children (aged 3-7) make when performing TrackIt, to better understand factors driving improvement in performance over age. In addition, we manipulated parameters within TrackIt to vary demand on children’s SSA, and measured behavioral performance over age. Our results also help suggest appropriate parameter settings for calibrating TrackIt to different age groups.