This research examined the accuracy and power of sex, social class and ethnic stereotypes in person perception. Participants included 49-56 teachers and nearly 2,000 students in seventh-grade public school math classes. Results indicated that teacher perceptions regarding achievement and motivation differences between girls and boys, lower and higher social class students, and African American and White students were mostly accurate. Results also showed that although teachers generally relied on students’ personal characteristics to form their perceptions, they occasionally relied on stereotypes. We discuss these results in terms of the classic view that stereotypes are inaccurate, rigid, exaggerated and exert powerful effects on person perception.