Zearn Math is a popular software platform for K-8 mathematics learning, designed to enable all students to successfully access grade-level content. RAND researchers collaborated with Zearn, the product's developer, to design this evaluation. Then RAND conducted the study independently, randomly assigning 64 schools in an urban Texas district to either supplement classroom instruction with Zearn Math in grades 3-5 for two years -- or to continue with business-as-usual, which included various other supplemental technology products. High proportions of economically disadvantaged, Hispanic, English-learner, and below-proficient students made up the primary sample of 10,000+ students. The study preregistered two confirmatory research questions about Zearn Math's effects on Texas STAAR math assessment scores, for all students and students below proficient at baseline. Those results were positive but not statistically significant; equivalent to raising a control group student from the median to the 53rd or 54th percentile. Although this study did not yield confirmatory evidence that Zearn Math improves student learning, consistent positive signals across all estimated confirmatory and exploratory effects, including on the MAP adaptive mathematics assessment, suggest it holds promise to do so.