One-parent families are a growing family form, most often characterized by father absence. Of a representative sample of about 9000 Swedish schoolchildren born in 1967 (the UGU project), 82% lived with their two parents, 15% with their mother and only 2% with their father, according to the 69% of parents who answered a questionnaire. Controlling for parental education, at age 13, children living with their mothers scored lower than those with two parents on various measures of educational aptitude and achievement. The differences were larger for girls and larger in mathematics than in verbal measures. At age 21, subjects who had lived only with their mother had less often selected and completed a theoretical course at upper secondary school (for boys particularly less often a technical course) and more often had completed no education after compulsory school. Thus low achievement in the mathematical-technical sphere, typical of 'masculine' orientations, characterizes children with no father in the home.