Researchers have estimated that by 2030, two of every five American public school students will be acquiring English as second language learners (Shah & Cavanagh, 2012). Providing adequate means by which ELLs can obtain both English language and academic proficiency will be paramount if they are to be successful, contributing members of their communities. Thus, this study was designed to explore the impact of Arizona's current instructional mandates (Ariz. H.R. 2064 and Ariz. Rev. Stat. § 15-751 -- 15-756) on the academic progress of English Language Learners (ELLs) in reading. Two administrations (2012 and 2014) of the reading subtest of the Arizona's Instrument to Measure Standards (AIMS) annual assessment were used to compare the third and fifth grade reading achievement of ELLs to that of mainstream students. The sample was comprised of 322 fifth grade students from a southwest Arizona school district. The sample included 64 ELL students who were enrolled in the school district continuously from kindergarten through fifth grade and 258 mainstream students who were educated within the district for third through fifth grade. Results of the one-way Analyses of Variance (ANOVA) and subsequent post hoc analyses revealed statistically significant differences in student achievement. ELLs who participated in the Structured English Immersion (SEI) program for three years or more by grade 3 and four or more years by grade 5, respectively, scored significantly lower than mainstream students on both administrations. Thus, the current SEI model mandated by the state of Arizona is not sufficiently supporting all ELLs. [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.]