Abstract
From a study of 600 premature and mature children from 6 months to 2 years of age, it is concluded that mean development quotient falls steadily with decreasing birth weight at all ages, and twins show lower scores than singly born children. Development ability is related to the apparent intelligence of the mother. First born children attain higher developmental scores than later born children. The incidence of symptoms suggestive of cerebral birth injury increases with decreasing birth weight. At 2 years, the mental ability of children of like birth weight with and without such symptoms does not differ.