There is growing evidence that the COVID-19 pandemic had a large and negative impact on student learning. This dissertation explores the effect of the pandemic on one of the most vulnerable student subgroups: English Learners (ELs). In this work I examine existing disparities among subgroups of ELs, and the different ways the pandemic has impacted these disparities. These language learners' academic English proficiency, determining their status as an EL, is examined within the context of individual, institutional, and dynamic factors that have shaped and continue to impact these students' educational experiences and trajectories in American classrooms. Leveraging population-level longitudinal data from ACCESS Online -- an annual "high-stakes" language proficiency assessment administered across member states in the WIDA Consortium, I present evidence from regression models with increasing complexity that account for (a) the clustering of millions of students across thousands of schools, districts, and WIDA states, (b) individual-level factors such as students' time as EL, "newcomer" and "long-term" status, ethnicity and race, gender, disability status, interrupted education, migrant status, and parental refusal of language support services at school. Consistent and precise estimates from multilevel regression models highlight and document large disparities in the average English proficiency of ELs across several demographic subgroups, and provide timely and detailed data on the detrimental, differential, and ongoing impact of the COVID-19 pandemic on many young learners' academic outcomes. For example, students identified as Hispanic, making up most of the EL population, report substantially lower average proficiency compared to non-Hispanic identified ELs; the findings show that this disparity has further increased after COVID-19. The uncovered disparities in proficiency between EL student subgroups representing multiple ethno-racial and other overlapping identities are interrogated under the theoretical lens of Intersectionality (Crenshaw, 1991), to identify, contextualize, quantify, and shed light on historical, political, and structural inequities in educational opportunities that result in systemic and persistent differences between academic outcomes. The Intersectionality framework, stemming from legal studies of Kimberle Crenshaw, informs the complex and varying ways the pandemic has impacted English Learners' education, exacerbating the already-substantial disparities. The evidence shows some modest recovery for select EL subgroups; newcomer ELs and English learners across all racial identification categories report higher average scores than prior to the pandemic unless they also were identified with Hispanic ethnicity. Making up the majority of EL student population nationally, the findings emphasize the need for a more careful focus and more effectively designed support systems for these English language learners, who are consistently underserved and are falling further behind. [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://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]