Research Findings: The purpose of this study is to advance our understanding of student-teacher ethnoracial matching in early elementary school by exploring two executive function outcomes -- working memory and cognitive flexibility. Drawing on nationally-representative, longitudinal sample of kindergartners (N = 18,170) from the Early Childhood Longitudinal Study -- Kindergarten Class of 2011, we relied on a fixed effects methodology and found student-teacher ethnoracial matching benefits on working memory skills, though not on cognitive flexibility. Observed associations for working memory are of similar size to those for academic achievement outcomes and are largest for Black and Latinx students. Policy or Practice: The benefits of student-teacher ethnoracial matching on academic outcomes--ranging from academic achievement to postsecondary attainment--are well documented. Yet, we know far less about the role of student-teacher ethnoracial matching on human development. This study helps to address this missing understanding of the importance of teacher diversity in supporting students' outcomes.