This research investigates grades kindergarten - 5 English as a Second Language (ESL) and General Education (GE) co-teachers' perceptions of one another's roles, strengths, and areas for improvement in co-teaching academic language and content to English language learners (ELLs) in the GE classroom. Theories of social constructivism and cooperative learning guide this study, which approaches co-teachers' perceptions as a function of how they make meaning of their social interaction and experiences (Vyogotsky, 1978; Villa, Thousand, & Nevin, 2004). Using QUAN-qual sequential explanatory design, this descriptive study uses survey methodology and small-scale follow-up interviews to create an illustrative, descriptive portrait of ESL and GE teachers' perceptions of one another's roles and professional development needs. Quantitative and qualitative survey results are triangulated with qualitative interview findings. The integrated findings illuminate the areas of convergence and divergence in ESL and GE teachers' perceptions as co-teachers of ELLs in the GE classroom. The main conclusions are discussed with regard to existing literature on co-teaching. Overall, ESL and GE teachers appeared to have a general understanding of one another's roles, yet some perceptions diverged with regard to sharing responsibilities and whether the GE teacher was the "primary instructor". In addition, this study concludes that despite availability of some common planning time, co-teachers frequently desired to improve the quality and quantity of their co-planning, co-teaching, and reflection on students' needs. Co-teaching strengths that were identified include openness, flexibility, and the ability to differentiate instruction. However, in order to improve co-teaching, both ESL and GE teachers perceive the need to gain skills and knowledge in one another's areas of expertise. Data analysis shows that co-teachers' desired professional development topics and types of offerings interrelate thematically with perceived strengths and areas for improvement. The study concludes with a discussion of implications for school administrators and teacher educators, including pre-service teacher educators, who want to support ESL and GE co-teachers. The discussion also addresses the implications for ESL and GE teachers whose co-teaching practice may benefit from reflection on the findings of the study. Finally, directions for future research emanating from this study are offered. [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.]