The impact of only child peers on students? cognitive and non-cognitive outcomes

We utilize representative and randomly assigned class data in China to study how being integrated with class-mates who are only children in a family affects students' academic and non-cognitive outcomes. A single child has certain common characteristics related to social preferences and learning attitude, which will potentially change the classroom environment. Our findings show that having a 10-percentage-point increase in the pro-portion of only child peers in the classroom improves students' test scores by 6.78% of a standard deviation. However, when facing a higher share of only children, students' mental health and social development will de-crease. A somewhat more interesting finding is that only children appear to suffer more from having only child peers than students with siblings regarding social development. A further decomposition of mechanisms suggests that teachers' teaching strategy, student-parent interactions, and student-student interactions explain a total of approximately 32.52% of this effect on test scores, and the lack of student-student interactions accounts for approximately 22.50% of the loss of social development at school.