Changing demographics, student diversity, and increased accountability have compelled educators to challenge the uniform constraints of traditional instruction and create an environment focused on individual achievement. Differentiated instruction empowers teachers to target multiple learning styles through varied themes, adapted content delivery, and assessment options. This quantitative quasi-experimental research study examined the effects of differentiated instruction on seventh grade student performance on standardized mathematics assessments using a repeated-measures design. Two independent research trials, controlling for initial group differences with 2011 Texas Assessment of Knowledge and Skills (TAKS) scores, provided inconclusive assessment results. Significant differences between students who received differentiated instruction compared to students who were instructed using traditional lecture-based strategies were inconsistent for each research trial. All learning groups, including special education, economically disadvantaged, English language learners, and gifted were included to determine if strategies were successful based on specific learning needs. Evidence obtained through classroom observations revealed deficiencies in effective instructional delivery of differentiated strategies, emphasizing the need for ongoing, quality professional development and support for educators. [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.]