The purpose of this study was to examine the impact of teacher education and professional development on teachers' perceptions of efficacy with providing effective English language instructional support to English learners. Using Bandura's (1997) self-efficacy theory, this study also analyzed the relationship between perceptions of efficacy and observable classroom practices. A qualitative methods approach was used for this study. Data about pre-service and in-service teacher preparation, perceptions of efficacy, and classroom practice were collected using surveys, interviews, and observations. The data revealed that teachers' perceptions of efficacy were increased when there were opportunities for active learning and collaboration during their teacher education programs and professional development experiences. In addition, a constant shift in focus with how to best support English learners limited the impact that teacher education programs and professional development had on teacher efficacy. Finally, the teacher with more intensive language acquisition and development training (i.e., Dual Immersion teacher) was more readily positioned to implement learned research-based instructional practices than those teachers who did not have the same training. The results of this study led to the following implications for practice. First, in order to increase teacher efficacy, teacher education and professional development must provide pre-service and in-service teachers with opportunities to actively engage in their learning as well as collaborate with their colleagues. Second, teachers must increase their knowledge of educational linguistics and effective English language instructional strategies to support the English learners in their classrooms. [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.]