The purpose of this research study was to determine if there is a relationship between the implementation phase of Response to Intervention (RTI), an academic multi-tiered system of support, and eighth grade students' mathematics, reading, and science Minnesota Comprehensive Assessments (MCAs) proficiency achievement. Data for this study were collected using a RTI phase survey sent via Qualtrics to Minnesota middle school principals and publicly accessible MCA proficiency data via the Minnesota Department of Education (MDE) website. The researcher analyzed data using the Statistical Package of the Social Sciences (SPSS). Each principal's survey response was aligned with the school's eighth grade students' achievement results as measured by the MCAs. A Pearson r analysis was completed to determine if a relationship existed between the variables. There was no statistically significant (p > 0.05) relationship between implementation stages of RTI and eighth grade students' mathematics and science MCA proficiency achievement in Minnesota middle schools. There was a statistically significant (p < 0.05) and positive relationship between the implementation phase and eighth grade students' reading MCA proficiency achievement in Minnesota middle schools. [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.]