This study aimed to investigate the features of only child status related to physical health, mathematics achievement, and school feelings and expectations from a different perspective. A representative sample of 91,619 Grade 4 students with an average age of 10.4 ± 0.7, among which 28,631 were only children, were assessed. We used propensity score matching and the average treatment effects on the treatment to analyze data. The treatment was the only child of a family. The results indicated that only children (...) have better academic achievement and school feelings, while non-only children have better physical status and anaerobic fitness. In addition, gender and rural vs. urban areas differences were also explored. The adverse situation for rural only boys is emphasized for families, researchers, and governments to focus on. Some suggestions are given under the Two- and Three-Child Policy. (shrink)