The purpose of this quantitative comparative study was to determine the existence or nonexistence of performance pass rate differences of special education middle school students on standardized assessments between pre and post co-teaching eras disaggregated by subject area and school. Co-teaching has altered classroom environments in many ways. As teachers' instructional roles evolve to accommodate the needs of general and special education students, general education teachers are required to deal with these increasing challenges, while simultaneously having to meet the demands of heightened accountability measures. Archived special education performance passing rates of the Georgia criterion-referenced competency tests (GaCRCT) regarding content area of English/language arts, math, reading, science, and social studies for the 2007-2008 school year (pre co-teaching) and from 2008-2009 through 2014-2015 school years (post co-teaching) from 8 middle schools were analyzed using t-tests to determine if there were any statistically significant differences. The occurrence or nonoccurrence of co-teaching served as the independent variable and the GaCRCT pass rates were treated as the dependent variable. The findings from this research were used to determine that co-teaching did not significantly impact overall student achievement as academic improvements were inconsistent across grade levels and content areas. The main conclusions drawn from this study were that co-teaching instructional impact was most noticeable in science and additional quantitative research is needed to validate whether co-teaching as an instructional strategy best suits the academic needs of special education 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://www.proquest.com/en-US/products/dissertations/individuals.shtml.]