The purpose of this evaluation was to examine the impact of i-Ready Personalized Instruction that met Curriculum Associates' recommended usage levels on ELA achievement, as measured by the Massachusetts Comprehensive Assessment System (MCAS) ELA assessment. This study compared the ELA achievement growth in the 2020-21 school year of students who used i-Ready Personalized Instruction with fidelity in ELA classrooms to that of students who used the i-Ready Diagnostic Assessment suite, but did not have access to Personalized Instruction. Hierarchical Linear Modeling (HLM) was used to compare ELA achievement gains, and analyses were performed by grade level. Results showed that students in Grades 4 and 8 that used i-Ready Personalized Instruction with fidelity had significantly larger MCAS ELA achievement gains than did comparison students who did not use Personalized Instruction. Additionally, ELA achievement gains for students in Grades 5 and 7 that used i-Ready Personalized Instruction, in relation to those of comparison students, approached statistical significance (p < 0.10). These results help to show the importance of students using the Personalized Instruction suite with fidelity in order to maximize potential benefits of this program.