The moment a child walks into a new classroom, teachers and classmates form an impression based on minimal information. Yet, little is known about the accuracy of such impressions when it concerns children's social functioning at school. The current study examined the accuracy of children's, teachers' and adults' impressions of 18 unacquainted children based on thin slices of behavior. The likeability, popularity, prosocial behavior, aggression, and exclusion of these children were judged by 101 children, 79 elementary school teachers, and 68 young adults based on 20-second video clips. Judges were better than chance in predicting popularity and prosocial behavior, but worse than chance in predicting aggression and exclusion. Female judges were more accurate judging social exclusion of same-sex than other-sex targets. Teachers were more accurate than children in their judgments of prosocial behavior. The current study shows that confidence in one's impression of aggression and exclusion in unacquainted children based on minimal information is not warranted. KEYWORDS Accuracy; children; social functioning; teachers; thin slices THE MOMENT A CHILD walks into a new classroom, teachers and classmates form an impression. However, it is unclear how accurate such impressions are. As these types of impressions are the basis of subsequent expectations and behavior toward that person (Ambady et al., 2000), inaccurate impressions may be the prelude of negative social interactions. The current study therefore examines the accuracy of children's, teachers', and adults' impressions regarding a child's social behavior and status in the classroom context. Impressions of Children Numerous studies have examined the reliability of the impressions people form about an unacquainted adult (Hall et al., 2016). Even when these impressions are based on observations of less than 5 minutes, so called 'thin slices', studies have shown that people's initial impressions of a person's personality, political preference, and sexual orientation are quite accurate. (see Ambady et al., 2000 for an overview). Yet, it remains unknown whether peopleadults and age matescan also accurately estimate children's social behavior and status. Previous studies regarding impressions of children predominantly focused on children's academic behaviors. These studies showed that teachers quickly form impressions about hypothetical as well as their own students' future academic behavior and performance (Ritts et al., 1992; Rubie-Davies, 2018). These impressions are based on a variety of characteristics, including