The United States currently lags behind globally in the areas of math and science. In order to compete and meet the skills necessary for the future workforce, it has become necessary to seek out instructional strategies that will increase student achievement in those academic areas. With the wide variety of diversity occurring in public schools today, there is a need to identify how to best meet and challenge our students academically in order to close the achievement gap between different genders, ethnicities, socioeconomic status (SES), and ability levels. The purpose of this study was to determine the effects of accelerated mathematics instruction on the student achievement of heterogeneous groups of sixth graders as measured on standardized assessments. In addition, this study looked at individual effects on subpopulations including special education, gifted, ethnicities, genders, and low Socio- Economic Status (SES). The research design methodology used was quasi experimental non-equivalent groups. The study took place in a suburban school district located in the Southwestern United States comprised of over 32,000 students. Control and experimental groups were compared utilizing quantitative data collected from the mathematics subsection on the Arizona Instrument to Measure Standards (AIMS). The study compared heterogeneously grouped sixth grade students at six schools using quantitative data collected for three years, from 2010-2012. The control group presented on-grade level mathematics curriculum to their sixth grade students. The experimental group accelerated the mathematics instruction of their students by one year or equivalent of seventh grade level. The findings indicated there was a statistically significant difference between the control and experimental groups for the areas of SES, special education, gifted, gender and ethnicity. These data suggest that students taught a year ahead of their grade level, benefitted from this treatment rather than receiving the standard sixth grade mathematics instruction. As a result of this study, teachers may be able to determine whether to include more students of varying ability in higher level mathematics courses rather than isolating advanced instruction to high ability students only. The study findings will also assist in identifying whether the acceleration method of instruction has any effect in order to be considered an option to the traditional method of remediation for low achieving 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.]