Abstract: A sample of 146 first grade and 171 fifth grade only and non-only children from 7 schools in Guangzhou were given 11 cognitive tasks to investigate the difference in cognitive abilities which may exist due to the special condi- tions caused by the Chinese single-child family planning program. First grade only children scored higher in verbal memory and general information than non- only children. There is a general superiority of only children in tasks related to general cognitive abilities. Grade five only children do not exhibit superiori- ty in cognitive abilities. There is a general trend that male only children scor- ed better than female only children in the general information task. The super- iority of first grade only children over non-only children was explained by higher parental investment of only children. The decrease in cognitive su- periority of only children over non-only children for fifth grade children was explained by the process of maturation and schooling.

Key words: Only children, Non-Only children, Transient cognitive superiority, Children's performance on cognitive