English Language Learners (ELLs) represent the fastest growing population of K-12 students in the United States (National Education Association, 2020). This study sought to examine and improve the teaching practices used with newcomer ELLs at a high school in New England, USA, and respond to the question: How can newcomer ELL Students with Limited or Interrupted Formal Education (SLIFE) be provided with an equitable, accessible, and culturally responsive education? Two cycles of action research were conducted based on Stringer's (2014) approach to the action research process. Cycle 1 consisted of interviews and focus groups with administrators, teachers, and ELL students; a survey of high school teachers; and the analysis of documents related to ELL programming. The evaluation of Cycle 1 data led to the implementation of the Cycle 2 action step which utilized the structure of a Professional Learning Community (PLC) to deliver targeted professional development and build the capacity of teachers to teach newcomer ELLs in their mainstream classrooms. Participants in Cycle 2 worked with the researcher to direct the action step and engage in new learning focused on Culturally Responsive Pedagogy (CRP), English language proficiency standards, and the Sheltered Instruction Observation Protocol (SIOP) model. Student surveys and a focus group with PLC participants were used to evaluate the effectiveness of the action step. Findings suggest that the PLC format is an effective way to deliver professional development and increase teacher capacity to teach ELLs if the content of the professional development is readily transferable to classroom practices. Additionally, the findings suggest that existing resources can be adapted to provide ELLs with an effective education. These findings have implications for small school districts with limited resources that seek to improve ELL education in their contexts. [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.]