Based on the Chinese General Social Survey 2006 and 2008 data,this paper assesses the influence of the family planning policy on the qualitative development of children using education attainment and individual income of only children versus children with siblings as parameters.Our results show the following:(1)only children are better-educated than their counterparts with siblings;(2)only children earn higher income in comparison to their counterparts with siblings;(3)the income and education gaps between girls with and without siblings are greater than those between boys;(4)the education gaps between only children and children with siblings are greater for those born in the 1970s,but the income difference between only children and children with siblings is only significant for those born in the 1980s;and(5)the income and education gaps between only children and children with siblings are higher in urban regions.Results indicate that families with only one child invest more resources in children's quality under the family planning policy,which is consistent with the “quantity-quality trade-off” theory proposed by Gary Becker.