A number of capacity-building efforts are designed to assist teachers in meeting the needs of English Language Learners (ELLs), including supplemental certification and the Sheltered Instruction Observation Protocol, or SIOP Model (Echevarria, Vogt, & Short, 2008). The purpose of this study was to determine if the method for preparing teachers affects the teacher efficacy of mainstream teachers working with ELLs. Specifically, the study examined the teacher efficacy of teachers working with ELLs with no specific preparation to those who have participated in SIOP Model training and to teachers who have earned supplemental certification. Participants in this study were mainstream teachers in Texas who teach ELLs. The Teachers' Sense of Efficacy Scale (Tschannen-Moran & Woolfolk Hoy, 2001) was used as the measure of teacher efficacy. The scale was modified by inserting the descriptor "English language learner" in place of the word "student." One-way analysis of variance was conducted to evaluate the relationship between the scale score variables and method of teacher preparation for serving ELLs. Teachers who reported the highest efficacy mean scores were teachers who had both supplemental certification and had participated in SIOP Model training. Results indicated that there is a significant difference between overall efficacy, efficacy in student engagement, and efficacy in instructional strategies of teachers of ELLs based upon their method of teacher preparation for serving these students for teachers who had supplemental certification and SIOP Model training, for those with SIOP Model training alone, for those with certification alone. In the area of classroom management, results were significant for teachers who were both certified to teach ELLs and SIOP Model trained, and for those with SIOP Model training only. Results were not significant for those with certification alone. The results from the study demonstrated the need for teachers who serve ELLs to earn supplemental certification and to participate in high quality professional development models such as the SIOP Model. [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.]