Morrisania College Preparatory Academy (MCPA) is a small middle school comprising Grades 6-8 located in the Bronx, New York, which offers full integrated co-teaching (ICT). MCPA struggled with mathematics achievement for the first 3 years of its operation. To improve student outcomes in mathematics, the vice principal assisted with all classroom planning responsibilities for one math team each year for 3 consecutive years and co-taught one section with each team. A prototype of the intervention was conducted during the 2018-19 school year with the eighth-grade algebra team and then the intervention was provided to the eighth-grade algebra team during the 2019-20 school year. During the 2020-21 school year, the intervention was provided to the seventh-grade math team, and the eighth-grade algebra team was monitored for intervention sustainability during the post-intervention year. To determine intervention effectiveness, the four subject teachers participated in 60-min qualitative interviews, which were analyzed utilizing the framework approach. Student achievement data for eighth-grade algebra for the intervention and post-intervention years were compared to data from the successful prototype year. Student achievement data for seventh-grade math were compared to a control group of the same students as sixth graders and to a control group of different seventh graders from the previous year. Results showed that the intervention improved student outcomes and, to a lesser extent, impacted teacher instructional practices. All teachers interviewed reported the intervention to be beneficial. The intervention also provided the vice principal with better insight into the school's instructional systems, increasing his job effectiveness. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]