The problem that was investigated in this study was that despite existing implementation of reading instruction strategies, some students in fourth grade demonstrate reading difficulties prompting the need for additional approaches to reading instruction. The purpose of this quantitative quasi-experimental study was to investigate the difference in fourth graders' reading achievement growth as measured by the i-Ready test between students who participated in the online Reading Plus program and students who participated in business-as-usual reading instruction. The theoretical foundation is applied behavior analysis, which involves using strategies derived from behaviorism theory to improve learning. Aggregated and de-identified i-Ready scores were collected for the 49 fourth grade students at the target school and 43 fourth grade students at the school providing business-as-usual reading instruction. The standardized mean difference was used to determine baseline equivalence between the Reading Plus group and business-as-usual group using the i-Ready scores at the outset of the study. An independent samples t test comparing the two groups on i-Ready scores at the outset and conclusion of the study was calculated to determine differences between scores of the target and business-as-usual students. Cohen's d was used to determine if results show practical significance. Cohen's d was 1.23, which indicates a large, standardized effect size, meaning that the research finding has practical significance. The findings may promote social change by addressing the reading development of many Grade 4 students; the local school has elected to use Reading Plus program for 1 year in hopes of providing additional individualized adaptive instruction for students who struggle with reading. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]