Participants completed long single digit sums in two interactivity contexts. In a low interactivity condition sums were solved with hands down; in a high interactivity condition participants used moveable tokens. As expected accuracy and efficiency were greater in the high compared to the low interactivity condition. Participants were profiled in terms of working memory capacity, numeracy, math anxiety and expertise in math. All of these measures predicted calculation errors in the low interactivity condition; however, in the high interactivity condition, participants’ performance was not determined by any of these variables. We also developed a scale to measure task engagement: Participants were significantly more engaged with the task when they completed the sums in the high interactivity condition. However engagement level did not correlate with calculation error. Interactivity transformed the deployment of arithmetic skills, ameliorated performance, and helped reduce the difference in performance between individuals of low and high math expertise.