The current study employed a randomized controlled trial to evaluate the use of peer tutoring and fluency-based instruction to increase mathematics fluency with addition and subtraction computation skills. Forty-one elementary school students between the ages of eight and 12 years participated in the 8-week study using cross-age peer tutoring, Say All Fast Minute Every Day Shuffled, frequency building, and the morningside math facts curriculum (Johnson in Morningside mathematics fluency: math facts (vol 1-6; curriculum program), Morningside Press, Seattle, 2008). Pre- and post-test measures of mathematics fluency and calculation were conducted with all participants. A measure of social skills and competing problem behaviors was also conducted at pre- and post-testing to evaluate any additional effects of the peer tutoring model. The results demonstrated a statistically significant difference between groups on measures of mathematics fluency, with the experimental group demonstrating significantly higher scores than the control group at post-testing. There were no significant differences between groups on measures of social skills and competing problem behaviors or calculation. The findings indicate that cross-age peer tutoring and fluency-based instruction resulted in positive outcomes for tutees in the mathematics domain, specifically mathematics fluency.