As the number of English learners (ELs) in the U.S. continues to rise, and the push for inclusion models grows, so too does the need to prepare mainstream teachers to educate this diverse population of learners. However, most mainstream teachers lack the specific theoretical background and skillset necessary to provide optimal instruction for ELs. This dissertation describes an exploratory multicase study, combined with ethnographic methods, that features three mainstream teachers' experiences as teachers of ELs in a Queens, New York City elementary school. Data sources included monthly interviews, teacher observations, and weekly teacher-kept journals. I arrived at three themes: (a) mainstream teachers attempted to create a supportive environment for ELs; (b) mainstream teachers experienced social, institutional, and personal challenges related to teaching ELs; and (c) mainstream teachers struggled to recognize, identify, and teach to ELs' needs as English learners. Based on these findings, foremost, teachers of ELs need to develop multilingual awareness--a sense of the ubiquity and power of language in thought and human interaction--in all contexts. For teachers to develop multilingual awareness, school-based professional development and teacher training programs must include implicit bias training and Second Language Acquisition (SLA) theory. Implicit bias training should focus on the impact of teachers' perceptions on their thoughts, actions, and interactions involving students, as well as the influence of personal ideology and social-structural contexts of education. Furthermore, districts and schools must consider the structural constraints related to scheduling, planning time, and parent communication in creating school policy. [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.]