As students return to school after the holiday break, some feel more comfortable back in the classroom than others. Kids develop images of themselves as “smart” or “not smart” at very young ages. In 2012, Beth Hatt wrote about a year she spent studying a kindergarten classroom to figure out how that happens.

For her study, Hatt picked a southern town, where children of academics mixed with working-class kids. In the class, 15 of the students were white, and the other 10 were black. The teacher, who Hatt identifies as “Mrs. Rayburn,” and the teaching assistant, “Mrs Daniels,” were both middle-class white women.

Hatt found that her own initial assessment of how “smart” students were—based on their academic knowledge—differed from Mrs. Rayburn’s. The teacher seemed to assess students largely based on their behavior and their class and race backgrounds. For example, the student with the highest pre-K assessment score was a poor, white boy with a mild speech impediment. Hatt writes that the teacher “openly held very low expectations for him” and referred him for tutoring, leading him to develop a dislike of school.

The students also developed ideas about smartness that were tied closely to the teacher’’s assessment of their behavior. For them, this revolved around “the stoplight,” where each student was represented with a car that began on green but would be moved to yellow or red if they misbehaved.

“When I interviewed students, I discovered every child defined being smart as ‘not having to move your car,'” Hatt writes.

Talking to parents, she found that the first thing kids often talked about after school was who had to move his or her car that day.

Overwhelmingly, the children identified a black boy from a low-income household, “Jackson,” as the student who “always moved his car” and, thus, was “not smart.” Hatt found that Jackson had difficulty adjusting to the classroom expectations to stay still and keep quiet unless called on, but that he very much wanted to do the “smart” thing and comply with his teacher’s expectations. She describes one incident in which he became upset after having to move his car to yellow and was then further punished with a time-out when he was unable to stop crying loudly.

In contrast, students identified “Natalie”—a middle-class, white girl whose background presumably prepared her well for a classroom run by middle-class, white women—as the “smartest” kid in class.

Beyond their behavior itself, Hatt found Mrs. Rayburn was more likely to identify misbehavior in black students, particularly boys, while white boys were not called out for rule-breaking.

While Hatt’s paper is limited to her experience in one classroom, she notes that the dynamics that lead to much of what she witnessed are common across the country. U.S. teachers are largely middle-class white women, and school cultures tend to reward the kinds of behavior that are typical of middle-class white households. Even the specific use of a “stoplight” type display that publicly advertises which students are, and aren’t, “smart,” is widespread.