This three-manuscript dissertation attempts to answer the question: "How does students' English language proficiency (ELP) inform the availability, structure, and use of English language accommodations and intervention to support the academic achievement of English learner (EL) students?" The question is addressed using three independent but related empirical studies. First, a systematic literature review was conducted to answer the research question: What are the most common EL assessment accommodations and ELP assessments, and what does the research say about their effectiveness? Then, an interventional, quasi-experimental study addressed the research question: To what extent do translated passages and word-to-word translation of language arts vocabulary terms affect EL students' reading comprehension performance when compared to their non-EL peers? Finally, a mixed-method correlational study addressed the research question: Is the ACCESS score predictive of EL students' reading abilities throughout the year it is used as measured by students' reading abilities according to the MAP reading assessment in the spring, fall, and winter administrations? Findings indicate that although EL students are not performing as well as their non-EL peers on content area assessments, providing EL students with opportunities to utilize their first language and English on assessments can allow students to show their true knowledge on content area assessments. Additionally, although ACCESS scores serve as an accurate representation of EL students' reading abilities for a year after the assessment, additional research could help provide a more in-depth or accurate depiction of EL students' abilities. Implications for teachers, school and district leaders, policies, and research are discussed. [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.]