Officals, media coverage and prevention programs have assumed that fathers of infants born to US school-age (10-18 years old) mothers are school-age peers. This study analyzes fathers' ages in 46 500 California births to school-age mothers in 1993, for which 85% of the fathers' ages were stated and whose distribution is similar to that of less complete national samples. Adult, postschool men father two thirds of the infants born to school-age mothers and average 4.2 years older than the senior-high mothers and 6.7 years older than the junior-high mothers. The extensive involvement of adult males in both school-age motherhood and its precursors represents a significant, undiscussed factor deserving greater attention.