Two competing hypotheses concerning the effects of stressful environments on the onset of puberty were tested using longitudinal data for a sample of boys from low socioeconomic backgrounds. Paternal alcoholism and maternal social position were used as indicators of family stress. School placement was monitored from school entry to 14 years of age. Teachers rated the boys' disruptive and anxious behaviors, while the boys reported on parenting behaviors at 10 years of age. Pubertal maturation, age of first sexual intercourse and sexual behavior were assessed between ii and 14 years of age. The prepubertal data indicated that boys with an alcoholic father, or a mother from a low social position, were more stressed and had more behavior problems: the boys with alcoholic fathers perceived their parents as being more punitive, and as setting fewer rules concerning their behavior; those who had at least one maladjusted parent were more often placed out of an age-appropriate regular classroom, and were rated more disruptive and more anxious by their teachers. Paradoxically, the results for the onset of puberty gave support to the two rival hypotheses. Paternal alcoholism led to a delay of male pubertal onset, as suggested by the hypo thesis that stress activates the hypo thalamic-pituitary-adrenal axis, and inhibits the hypothalamic-pituitary-gonadal axis. However, sons of alcoholic fathers had more frequent sexual intercourse and more sexual partners, as suggested by the evolutionary theory of socialization. High maternal social position acted as a protective factor for school placement of boys with an alcoholic father. These results challenged a key hypothesis of the evolutionary theory of socialization for males. They indicated that the link between childhood family environment, behavior development, pubertal maturation and sexual promiscuity are more complex than anticipated.