School-teachers were asked to assess the school achievement and behaviour of 45 children who had been small-for-dates (SFD) at birth, and of 19 control children who had had a normal birthweight. The SFD children were divided into groups according to the stage in gestation at which slow head-growth began. Those whose head growth had slowed before 26 weeks gestation achieved less well at school than those who had had no evidence of slow intra-uterine head-growth. Their teachers also thought they were less able to concentrate. Boys (but not girls) whose head growth had slowed between 27 and 34 weeks gestation also had problems at school. The authors conclude that school achievement and behaviour of children who were small-for-dates at birth is related to the severity of slow growth before birth, the sex of the child and the social class of the parents.