A Mixed-Methods Study of English Language Learners' Academic Achievments in a Spanish Language Immersion Schoo

English Language Learners (ELLs) represent the fastest growing population in the public-school community in the United States (U.S.), where their academic achievements lag behind their native English-speaking peers. English Language Learners' academic achievement gap has raised a challenging issue for U.S. educators. A convergent parallel mixed-methods study was conducted to 1) compare English Language learners' academic achievements (mathematics and English Language Arts [ELA] scores) to non-ELLs' academic achievements (mathematics and ELA scores) in a one-way Spanish immersion school in the Midwestern United States; 2) examine the impact of using Spanish as an instructional tool on English Language Learners' (ELLs) academic achievements who are admitted in a Midwestern Spanish language immersion school; 3) investigate how teachers perceive the effectiveness of Spanish language instruction on students' achievement and more specifically, ELLs; 4) assess the one-way immersion program's ability to assist ELLs' performance by using their first language and achieve better academic advancement compared to non-ELLs. The results of this convergent parallel mixed-methods study explained that there was no significant difference between ELLs and non-ELLs of mathematics and ELA scores. ELLs in a one-way immersion school perform similarly to their non-ELLs in measure of mathematics and ELA. Based on the results of this mixed-methods study, all teachers confirmed that it was an excellent idea to use ELLs' first language as an instructional tool. They insisted that L1 represented a great benefit for ELLs who learn through their L1. Also, ELLs can develop their first language besides acquire English as a second language.;Keywords: English Language Learners, language immersion program, one-way immersion, academic achievement.