As the population of English Learners (ELs) continues to rise in the United States, there is a need to investigate the efficacy of teachers who are assigned to instruct them. The purpose of this study was to examine the factors that contribute to teacher efficacy when mainstream elementary/middle school teachers instruct ELs while addressing the gap in the research that has not addressed the type of assistance (professional development in teaching ELs, administrative support, role of class size, and the assistance of a bilingual para-professional in the classroom during instruction) that benefits teachers while instructing ELs, potentially affecting their efficacy. Bandura's Social Cognitive Theory, focusing on self-efficacy, was the foundation of the study. Eighty-two teachers participated in this quantitative, purposive study using a Likert scale, Teacher Efficacy for Teaching English Language Learners (TETELL) survey, sent to six elementary/middle schools in a mid-Atlantic region school district with a large proportion of ELs to assess their beliefs of the issues faced when instructing ELs. Data was collected for two weeks then analyzed primarily by ANOVAs to evaluate the relationship between the independent variables and teacher efficacy resulting in a significant difference in means in teacher efficacy and EL training. ANOVAs run on the three subscales (Instruction/Classroom Management, Social Cohesion, and Motivation) revealed a significant difference in means in Instruction/Classroom Management and EL training and in Motivation and both EL training and class size. Implications for social change include the need for on-going EL training to assist teachers. [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.]