Using a causal-comparative research design, this study investigated the effectiveness of Differentiated Instruction Support Inclusion Services on fifth grade regular education and gifted students' Reading/Language Arts achievement. The study analyzed and compared the achievement of the regular education students who received no inclusion support services in 2009-2010 to those students who were in gifted inclusion classrooms in 2010-2011. Gifted students' Reading/Language Arts achievement was also analyzed for differences between samples. Tennessee Comprehensive Assessment Program (TCAP) scale scores from the 2009-2010 and 2010-2011 school years were utilized for this study. Students' fourth grade scores were used as a covariate to control for differences in base-line abilities. The main independent variable for the study was type of classroom: differentiated instruction support inclusion model vs. pull-out model. The dependent variable was students' Reading/Language Arts TCAP scores. The scale scores of participants came from five middle schools in one rural Tennessee County. All the schools in the study had similar demographics. Statistically significant findings indicated that the differentiated instruction support inclusion model had a positive effect on regular education students' Reading/Language Arts achievement. In addition, the findings from this study indicated that regular education girls had significantly higher achievement in inclusion classrooms when compared to the achievement of their male counterparts. No statistically significant differences were found for gifted students. Findings from this study indicate that regular education fifth grade students who participate in a differentiated instruction support inclusion classroom may increase their Reading/Language Arts achievement more than their peers who are in a general education class without differentiated instruction support. Since statistical significance indicated that girls perform better than boys in these classrooms, one recommendation is for teachers to provide non-narrative, informational texts such as magazines for boys in the reading classroom. In order to improve literacy, literature choices should be interest-based. A recommendation for further research is to perform a longitudinal study to evaluate the long-term effects of differentiated instruction support inclusion services on the Reading/Language Arts achievement of boys and girls. [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.]