The purpose of this study was to conduct a rigorous, external evaluation of the impact of the "Education Galaxy" Online Assessment, Practice, and Instruction programs on mathematics and reading achievement. Specifically, the study used a quasi-experimental (matched comparison) design that conforms with the requirements of the Every Student Success Act (ESSA) evidence standards for providing "Tier 2 Moderate Evidence." The outcomes of interest were grade-level gain (from third to fourth grade) on the mathematics and reading scales of the State of Texas Assessment of Academic Readiness (STAAR) assessment. Achievement gain of "Education Galaxy" user schools was compared to gain of non-user schools from the 2016-17 to 2017-18 school years, controlling for prior achievement and other school-level demographic variables to ensure baseline equivalence of the two groups. Results of the study revealed a positive impact of "Education Galaxy" on grade level gain from third to fourth grade on both mathematics and reading subscales of the STAAR compared to non-user matched comparison schools, with statistical significance levels (p-values) of <0.001 for mathematics and 0.068 for reading. The effect sizes of 0.58 and 0.30 for mathematics and reading, respectively, are considered "substantively important positive effects," according to What Works Clearinghouse Evidence Standards (WWC, 2017).