The purpose of this pretest-posttest comparative efficacy study was to analyze factors affecting literacy achievement of eighth grade middle school instrumental music students (n = 38) including (a) socioeconomic status (SES), (b) gender, (c) grade point average (GPA), (d) music motivation, (e) music involvement, and (f) instrument section. The findings of this study indicate that, utilizing the Iowa Tests of Basic Skills (ITBS) reading comprehension, reading vocabulary, and science subtests and the Northwest Evaluation Association (NWEA) Reading Measure of Academic Progress (MAP) as the dependent variables for each of the six independent variables, significant growth over time was made in each of the measures among all the groupings. Notable highlights from the study show that, in Post Hoc pairwise comparisons, large effect sizes were found for time and high SES students on the ITBS Science subtest, time and low SES students on the NWEA Reading MAP, time and male students on the ITBS Reading Comprehension subtest, time and high GPA students on the ITBS Reading Comprehension Subtest, time and high GPA students on the ITBS Reading Vocabulary Subtest, time and high GPA students on the ITBS Science Subtest, and time and low musically involved students on the ITBS Reading Vocabulary Subtest. While there were other large and moderate effect sizes, these named pairwise comparisons were all well over one standard deviation in effect. The results of the repeated measures analysis of variance statistical tests employed in this study indicate that there is an association between students' literacy achievement and participation in instrumental music. The findings from this research demonstrate that students who are actively engaged in music learning benefit from it and suggest that participating in music instruction also affects cognitive functions that influence other disciplines. [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/en-US/products/dissertations/individuals.shtml.]