Many elementary schools are shifting from traditional pull-out service models to push-in approaches, where multilingual learners collaborate with their English-only peers. However, research emphasizes the need for further investigation into implementing collaboration between elementary teachers and English Language Development (ELD) Specialists. This study examines how co-teaching and collaboration between these professionals influence the academic performance of English Learners (ELs) using The Collaborative Instructional Cycle (Honigsfeld & Dove, 2022). Specifically, it addresses perceptions of co-teaching, the impact of collaborative practices on effectiveness, the effect of weekly collaboration sessions on ELs' academic performance, and obstacles hindering collaborative co-teaching. A convergent, mixed methods study was conducted, involving collaboration sessions, pre- and post-surveys for teachers, and NWEA Reading MAP assessment scores. Four themes emerged from collaboration sessions: exploration of co-teaching models, positive reception towards co-teaching, delineation of skills and standards, and consideration of theme-based curriculum. Among the sixteen EL scores analyzed, 14 showed improvements in their NWEA Reading MAP Growth scores from September 2023 to December 2023, with 41% meeting their Fall to Winter Projected Growth goal. A statistically significant difference (p = 1.75) was observed, indicating a positive correlation between collaboration within co-teaching and ELs' academic performance. These findings underscore the effectiveness of collaboration and co-teaching in enhancing ELs' academic performance and fostering a professional environment in elementary classrooms. However, ongoing support and resources are crucial to facilitate effective collaboration and co-teaching among educators throughout the school day. [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.]