A robust body of literature has documented systematic parent-teacher discrepancies in ratings of children’s ADHD symptoms (inattentive, hyperactive, or impulsive behaviors) as a function of child race. Past research has suggested a potential role of teachers’ racial bias in higher ratings of Black children’s ADHD behaviors relative to Black parents’ ratings. The present study sought to better characterize these racial biases by examining implicit and explicit measures of racial prejudice and racial stereotypes, as well as Black parents’ perceptions of those biases as predictors of their ratings of Black children’s ADHD behaviors. Results suggested that white teachers’ explicit racial ADHD stereotypes predicted more biased ratings of Black boys’ ADHD symptoms. Moreover, perceptions of systemic racism predicted Black parents’ lower ratings of Black boys’ ADHD symptoms, relative to white boys. Finally, mediational analyses across the whole sample indicated that white teachers demonstrated more implicit racial prejudice than did Black parents, which in turn predicted more biased ratings of Black boys’ hyperactivity symptoms. No measures of racial bias predicted biased ratings of Black girls’ ADHD symptoms. Future research should aim to better understand the roles of these racial biases in assessments of other common types of childhood psychopathology, and develop interventions to reduce the impacts of racial biases in psychological assessments for children of color to promote racial equity in mental health care.