Black teachers are critical resources for children and schools. In experimental data, I document large effects of Black upper-elementary teachers on the self-efficacy (0.9 SD) and classroom engagement (0.7 SD) of their Black but not non-Black students, potentially driven by role modeling. Black teachers also benefit the test scores (0.2 SD) and absences (over 20% decrease) of all students--no matter their race/ethnicity--that often persist years later in high school. Furthermore, Black teachers bring unique mindsets and practices to their work (differentiated instruction, growth mindset beliefs, well-organized classrooms) that mediate a moderate to large share of effects on student outcomes. These findings help bridge the quantitative race/ethnicity-matching literature with theoretical discussion and qualitative exploration on why Black teachers matter.