The number of English language learners (ELLs) in the nation's classrooms is over five million, an increase of 57% in the last decade. California alone has 1.4 million ELLs in grades K-12 for the 2011-2012 school year, and one-third are secondary students who need to learn English and content in a very short time. These students usually come from lower socioeconomic backgrounds, have varied academic proficiencies, and generally attend schools with teachers unprepared to support their academic achievement. Moreover, teachers at the secondary level do not have the skills, knowledge, ability, or disposition to effectively instruct adolescent ELLs. The purpose of this qualitative study was to explore the perceptions of teachers who instruct ELLs in the secondary mainstream classroom and obtain insight into the preparation needed to effectively instruct ELLs in the secondary mainstream classroom. This qualitative study employed a grounded theory method to systematically collect and analyze the data. The data revealed teachers' feelings of inadequacy in the instruction of ELLs due to the inadequate training in their teacher preparation program, and these perceptions affected their attitudes towards ELLs. The findings in this study support the need for teacher preparation programs to redesign teacher education in order to support the academic achievement of the growing numbers of ELLs in the mainstream classroom. [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/en-US/products/dissertations/individuals.shtml.]