NExT LEVEL is a National Professional Development grant funded by the Office of English Language Acquisition, U.S. Department of Education. The grant partnered with three school districts and provided introductory training in working with English Learners (ELs) for select mainstream classroom teachers and teacher candidates; continued coursework for teachers to obtain add-on ESL certification; support for parents and families of ELs; and professional development for university teacher educators. The impact evaluation used a quasi-experimental design to determine the impact of the program on EL students' academic achievement in ELA and math. EL students who had a NExT LEVEL teacher for at least one class during the study period were compared to well-matched students in the same districts who did not have a NExT LEVEL teacher at any time during the study period. The two groups were assessed for differences in achievement outcomes on measures of standardized math and ELA after one year and after three years. In terms of ELA outcomes, there was a significant effect of NExT LEVEL after one year; however, the effect was in the opposite direction from what was expected. Comparison students had significantly higher one-year ELA achievement than the NExT LEVEL students. At three years, there was no significant effect of the treatment on three-year ELA outcomes. The one-year effect on mathematics was statistically significant, but with comparison students outperforming their NExT LEVEL counterparts. There was no significant impact on three-year mathematics performance. Several limitations of this study are discussed, including the mediating impact of the COVID-19 pandemic and the lack of data on teacher implementation of NExT LEVEL instructional strategies.