The development of 118 small-for-gestational age (SGA), 137 average-for-gestational age (AGA), and 118 large-for-gestational age (LGA) children was assessed at 7 years. The contributions of different factors to the variance in developmental scores were investigated by multiple regression analyses. All three groups showed the powerful influence of social class on intellectual ability at this age; and in the SGA and AGA groups the gross and fine-motor skills of girls were superior to boys. Smoking had a small effect in the AGA group, and in the two extreme groups first-born children did slightly better than later-born. Hypertension was associated with reduced scores in the SGA group, and LGA children who had spontaneous vaginal deliveries had higher scores than those delivered instrumentally or by caesarean section. There was a significant positive correlation between gestational age and developmental scores in the AGA group; but in the SGA group the relationship was in the reverse direction. Social class and sex affect the development of most children aged 7 years. Other factors seem to manifest an effect only under specified conditions.