Teacher collaboration has received international research attention and has emerged as an effective way for teachers to engage in professional growth opportunities (Dove & Honigsfeld, 2018; Rao & Chen, 2020). An examination of teacher collaboration can shed light on the process by which teachers work together and illuminate further possibilities for professional learning and growth across all English teaching contexts (Dove & Honigsfeld, 2018; Giles & Yazan, 2019). Building on a sociocultural theory of learning, this study examined ESL and science teachers' participation in a collaborative partnership to enhance ESL students' education. It investigated how both teachers learned to co-plan and co-teach ESL students in a seventh-grade science classroom in the Southeastern U.S. This study relied on qualitative data methods and employed grounded theory techniques (Charmaz, 2006). The findings showed that limited collaborative planning time and the ESL and science teachers' disparate notions of collaborative teaching contributed to the teachers' unequal collaborative planning and teaching roles. Consequently, different learning outcomes were realized for both teachers.