As advances in technology allowed national and state education assessments to be administered digitally, many school districts transitioned to computer-based instructional programs and assessments to improve student achievement and better prepare students for high-stakes computerized assessments. One such rural public school district in Mississippi implemented a supplemental web-based instructional program, i-Ready, for the first time in the 2017-2018 school year. The purpose of this study was (a) to investigate the effects of the i-Ready program on student achievement in Grades 4 – 5 reading/language arts and mathematics and (b) to determine if there were significant differences in growth (from pretest to posttest) among performance levels of students in Grades 4 – 5 on the 2017 state assessment in reading/language arts and mathematics. A quantitative research design using existing data was used to conduct the study, and the paired-samples t-test provided the primary means of analysis for research questions one and two to determine the effect of the i-Ready program on student achievement. The one-way analysis of variance (ANOVA) was used as the primary means of analysis for research questions three and four to determine if there were significant differences in growth among students across Performance Levels 1 – 5. The results from the research study showed the i-Ready program had a positive impact on student achievement in reading and math for Grades 4 – 5. No statistically significant differences were found in student growth among the performance level groups indicating all students were impacted by the program. Recommendations for future research include: (a) conducting longitudinal studies to determine long-term effects of participation in the i-Ready program, (b) analyzing methods of implementation by classroom teachers, (c) measuring i-Ready’s predictability of proficiency and growth on state assessments, and (d) conducting studies of other online instructional programs using control groups.