Based on the system theories approach, this case study investigated the collaboration process that took place among teachers working with newcomer English learners with disabilities. The significance of this study stems from the scarcity of literature on English learner newcomers with disabilities and the need for exploring collaboration among teachers and other professionals. The study utilizes Friend and Cook's (1990) ideologies about best practice in collaboration, which include trust, time, assessments, evaluation, and leadership. Qualitative data collection tools were used to examine aspects of collaboration at three different levels. These tools included classroom observations and semi-structured interviews with professionals. The study found that sustainability of effective teacher collaboration required a shared purpose and goal, open dialogue, a monitoring system, adequate resources, and frequent evaluations of student outcomes. The sense of unity of purpose was vital to creating positive interdependence among professionals. Triangulation ensured the trustworthiness of the data. Member checking and participant feedback were also employed to validate the findings. In the future, collaboration efforts will benefit from teachers receiving professional development to foster positive attitudes towards collaboration and to support appropriate use of time provided for collaboration. [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.]