<p>Increasing numbers of U.S. public school students speak English as a second language (ESL). Spanish is the language spoken most frequently by these students who are often identified as English Language Learners (ELLs). The increasing numbers of ELLs have heightened the demand for evidence-based ESL instruction and intervention. However, learning difficulties ELLs with language-based delays experience may be exacerbated in a bilingual instructional setting due to increased complexity, diversity, and quantity of verbal stimuli. These difficulties may be due to subtle inefficiencies in these ELLs’ cognitive processing mechanisms. Thus, this study is an investigation of the relationship among ESL instructional model, language proficiency, SES, and ELLs’ academic outcomes. Spanish-speaking kindergarten ELLs (<i>n</i> = 752) in a large and linguistically diverse public school district in Florida participated in this study. Hierarchical linear regression analysis reveals strong relationships among specific ESL instructional models, ELLs’ language proficiency, and their English academic performance from the beginning of kindergarten to the end of kindergarten. These findings challenge previous research and serve to inform ESL instruction and intervention policies and procedures.</p>