This qualitative study examined the experiences and perspectives of five high school teachers in a suburban area in Northern California. It investigated how each mainstream content teacher adapted their curriculum for their Newcomer Emergent Bilingual students. A Newcomer Emergent Bilingual student is one who has recently immigrated to the United States and has been in the country for less than two years. These students are placed into mainstream content classes in districts that have adopted the Structured English Immersion model, in which "nearly all" classroom instruction is in English. The theoretical framework in this study combines Shields's Transformative Leadership Theory and Jim Cummins's theoretical constructs on second language acquisition, Basic Interpersonal Communication Skills (BICS), and Cognitive Academic Language Proficiency (CALP). The data was collected through multiple classroom observations and one-on-one interviews with semi-structured questions. Guiding the study were the following research questions: 1) How are high school content area teachers implementing the SEI model? More specifically, how are they modifying their curriculum and instruction to meet the needs of Newcomer Emergent Bilingual students? 2) Are the strategies content area teachers are utilizing designed for Newcomer Emergent Bilingual students in their mainstream classrooms? In other words, are they utilizing instructional practices known to be effective with Newcomer Emergent Bilingual students? 3) What are teachers' perspectives and experiences regarding teaching Newcomer Emergent Bilingual students in their mainstream classrooms? The findings indicated that teachers are modifying their curriculum and instruction to meet the needs of Newcomer Emergent Bilingual students. They also demonstrated that they had transformative leadership qualities in recognizing the needs of their Newcomer Emergent Bilingual students and taking critical action by adapting their instruction to support student learning. Several of the educators in this study facilitated the effective use of research-based strategies to ensure their Newcomer Emergent Bilingual students had access to the content. They recognized that the current system places students in classrooms where all instruction is in English; therefore, they adapted their lessons to provide equitable access to the curriculum. While some educators expressed not having the support or professional learning to work with Newcomer Emergent Bilingual students, a key finding that emerged was the critical role that an ELD paraprofessional plays in the success of these students. Recommendations for district leaders, such as the superintendent, assistant superintendent, school board, and EL Specialist, include working collaboratively with agencies advocating for a curriculum that values the primary language and culture of Emergent Bilingual students. [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.]