This longitudinal, quantitative study examined the differences in second language acquisition among "first-" and "second-year" English language learners (ELLs) who attended newcomer and comprehensive middle schools. The study is organized into six cohorts by students entering middle school between 2006 and 2013 then graduating in 2013 through 2017. This study followed ELLs identified as "beginning" and "intermediate" English proficiency who are instructed in two different ESL program models: ESL content-based model (used in newcomer schools) and ESL pull-out model (used in comprehensive schools). The research will answer three research questions: (1) Are there differences in the average length of time to reach English proficiency, (2) Are there differences in exit level reading and math state assessments, and (3) Are there differences in high school graduation percentages. The literature review will show the latest research and the differences between the two ESL instructional models. Short and Fitzsimmons (2007) claim the true measure of language proficiency is not the result of a single assessment, but rather results after ELLs reach English proficiency. Findings from this study were reflected in the literature which aligned with Short and Boyson's (2012) research, which states that because ELLs have a variety of literacy skills, educational backgrounds, and social needs, there is no set newcomer model that best serves all 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://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]