Low achievement on standardized tests may be attributed to many factors, including teaching methods. Differentiated instruction has been identified as a teaching method using different learning modalities that appeal to varied student interests with individualized instruction. The purpose of this quantitative study was to compare whole-group instruction and differentiated instruction to determine which strategy was more effective to improve low achievement in a middle grade classroom. The study was guided by a framework of constructivism, multiple intelligence theory, and learning styles theory. The study was designed to answer the research question of whether there was a statistically significant difference between fraction and percent pretest and posttest scores of students in a math class that was instructed as a whole group compared to a math class that received differentiated math instruction. The study used a nonequivalent, quasi experimental design, with a convenience sample of 83 students. The data were analyzed with both paired "t" tests and independent "t" tests to examine the impact of differentiated mathematical instruction. Results demonstrated that students receiving differentiated instruction had a significantly higher performance in both fractions and percents units (p< 0.05), despite only mildly increased posttest scores. Further research is needed to explore and confirm the impact of differentiation as a teaching strategy in other areas of math, as well as in other content areas. This study contributes to social change by demonstrating to educators that instructional strategies adapted to different learning styles can enhance mathematical achievement of middle grade students. [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.]