This "Math Snacks" intervention measured 741 fifth grade students' gains in conceptual understanding of core math concepts after game-based learning activities. Teachers integrated four "Math Snacks" games and related activities into instruction on ratios, coordinate plane, number systems, fractions and decimals. Using a randomized, controlled, quasi-experimental design, classrooms were randomly assigned to one of two conditions in a delayed treatment model. First Group A, and then Group B, received 5 weeks of "Math Snacks" intervention in addition to the regular district mathematics curriculum. Using a carefully refined test containing multiple choice and open-ended items, both groups were assessed three times: prior to any interventions, at the end of Phase 1 (when only Group A had received the intervention), and at the end of Phase 2 (when both groups had received the intervention). Students' mean gains over 5 weeks were significantly higher while receiving the "Math Snacks" intervention as compared to the group not receiving the intervention.