In response to legislation from the federal government and the rising number of ELs in public schools many school districts are searching for ways to ensure ELs are making adequate progress on English proficiency. The problem is defining the best method for teaching ELs in the mainstream classroom is difficult. The current gap in educational research includes the absence of studies on specific training for mainstream classroom teachers. There is sufficient research on practices regarding delivery services for Teachers of English to Speakers of Other Languages (TESOL) services. However, there is little research on EL training provided to mainstream classroom teachers and the impact of that training. The purpose of this causal-comparative study was to test the andragogy theory that provided guidance on adult learning principles by comparing EL achievement in districts that provided targeted EL training for their mainstream classrooms teachers and those that did not in 2017-2018, 2018-2019, and 2020-2021 in terms of the districts English Language Arts (ELA) Missouri Assessment Program (MAP) scores for third through fifth grades in Missouri districts with an EL enrollment of 20 or more. Results from this study showed no statistically significant difference occurred in school districts that provided EL training to their mainstream classroom teachers and those that did not, however though not statistically significant, there was a slight increase in MAP scores for districts that had provided training. [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.]