English learners (ELs) in Florida face numerous challenges including low test scores, and high dropout rates, and are typically several years behind their peers when compared to other states. The purpose of this quantitative quasi-experimental ex-post-facto study was to compare the differences between ACCESS 2.0 scores of high school ELs in sheltered-model classes and inclusion-model classes in four high schools in two school districts in Northwest Florida. To examine the differences between sheltered-model classes that utilized an English language development (ELD) method and inclusion-model classes, the study was framed using sociocultural theory (SCT) and its constructs, mediation, regulation, internalization, and the zone of proximal development (ZPD) to measure language proficiency. The study sample included 150 ELs. Results from the independent samples "t" tests and Mann-Whitney "U" tests revealed positive statistically significant differences among the total composite scores (U = 1292, z = -4.697, p < 0.0005), among the listening scores (U = 1854, z = -2.063, p = 0.039), among the speaking scores (mean rank = 89.69; mean rank = 52.456), among the reading scores (M = 386, SE = 34, t(2.6) = 140, p = 0.011, d = 31.1), and the writing scores (U = 1456, z = -5.067, p < 0.001). The results may guide practitioners and policymakers by adding to the literature on ESOL program models. Additionally, the results may provide strategies for the identification of future program models in need of improvement leading to the implementation of educational activities necessary for narrowing the EL achievement gap. [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.]