This quantitative causal comparative study examined whether there were differences in American Indian student's test scores in Mathematics and English Language Arts between five schools in a school district in southwest United States. Archival data using students' individual test scores, including student demographics as grade level, gender, and ELL (English Language Learner) were also utilized. 172 third grade math students and 173 third grade English Language Arts students were used in the study. The theoretical framework of the instructional management model of instructional leadership called the Principal Instructional Management Rating Scale (PIMRS) conceptual framework by Hallinger and Murphy was used. Using one-way analysis of variance (ANOVA), the results for the math dataset was there is no significant difference in the third-grade student mean PARCC mathematics test scores among five elementary schools in the American Indian school district (ANOVA results, f [4, 167] = 2.05, p = 0.09, n[superscript 2] = 0.047). The ANOVA results for the English dataset was there is no significant difference in the third-grade student mean PARCC English Language Arts test scores among the five elementary schools in the American Indian school district (ANOVA results, f [4, 168] = 0.90, p = 0.46, n[superscript 2] = 0.021). This research study provided knowledge and addressed differences in students' performance outcomes in mathematics and English Language Arts in a diverse school district and location within a grade level. [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://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]