The purpose of this evaluation was to examine the impact of i-Ready Personalized Instruction on math achievement, as measured by SBA scores. We compared students in schools using i-Ready Personalized Instruction school-wide (Treatment students) and students who only received i-Ready Diagnostic assessments and who were in schools only partially using i-Ready Personalized Instruction (Comparison students). The study sample consisted of 5,330 students in 22 schools from Grades 3-6 from one school district in southern California. All schools used i-Ready Diagnostic assessments, but some schools were considered "full instruction" and assigned all students to receive both the Diagnostic and Personalized Instruction products. Students in these schools were compared to "diagnostic-only" students in other "partial instruction" schools where only some students received the Instruction product in addition to the Diagnostic product. (These Diagnostic and Instruction students in partial instruction schools are not included in this study.) Overall, this analysis presents promising evidence of i-Ready Personalized Instruction on student math achievement. This relationship between i-Ready Personalized Instruction and math achievement was strongest for students in Title I eligible schools, Grade 4, and among students who met the recommended usage guidelines. Future studies should seek to further examine the reasons behind this variation in usage.