Educational Research Institute of America (ERIA) assessed the instructional effectiveness of student math achievement for GO Math! for 803 students, Grades 3, 4, and 5 in ten different schools, over the course of one semester. A quasi-experimental, pretest-posttest design was employed to compare math performance among students using GO Math! (experimental group) to students using another mathematics program (control group). The results of this study indicate that use of the GO Math! program led to improved mathematics achievement over the course of the semester. Further, at all three grade levels, students using GO Math! had significantly greater performance at the end of the semester than students using other mathematics program, providing initial evidence of the instructional effectiveness of the GO Math! program in elementary school classrooms.