The purpose of this quantitative ex post-facto study was to determine if differences exist in 4th-grade students' reading and math learning outcomes between co-taught classrooms and traditional classrooms in a Florida public school district. The study was conducted with archival data from the school district's fall and winter progress monitoring results using a convenience sample of 4th-grade students who received instruction in co-taught or non-co-taught classrooms during the 2017-2020 school years. The two research questions asked if there were any statistically significant differences between 4th-grade students' math and reading learning outcomes between co-taught and non-co-taught classes. The sample size was 2,010 students in the math group and 1,936 students in the reading group. Learning outcomes were measured using scale scores from the i-Ready Reading and Math Diagnostic assessments. The results on the independent-samples t-test for RQ1 using effect size of 0.083 indicated that the results were not significant when (p <0.05), Group 1 M = 12.81 and Group 2 M = 13.95; 95% CI [12.01, 13.60], t (2008) = -1.935, (p =0.053), (d = 0.46). For RQ2, the results of the independent-samples t-test indicated that there was not a statistically significant difference (p = 0.250) between co-taught and non-co-taught classes in reading when (p < 0.05), Group 1 M = 12.89 and Group 2 M = 11.67; 95% CI [11.39, 14.39], t (1934) = 1.150, (p = 0.250), (d = 0.22). [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.]