The outcomes were assessed longitudinally. The control groups of 15 infants were examined every other week during the 1st yr and every 4th wk thereafter using ordinal, sensorimotor scales. The audio-visual intervention intended for the 2nd group of 10 infants was tape-recorded mother talk and music under the control of the infants and mobiles that the infants could activate; this plan was never adequately implemented. The 3rd group of of 10 infants received extra untutored human care. The 4th group of 10 infants received the audio-visual intervention intended for the 2nd group plus access to responsive inanimate materials. For the 5th group of 11 infants, the infant-caretaker ratio was reduced to 2 or 3 to 1 and the caretakers were taught the Badger program supplemented with procedures to foster vocal imitation and semantic mastery of body parts and other objects and events regularly encountered. Each successive group, excepting the 2nd, achieved the top steps of nearly all 7 of the ordinal scales at mean ages younger than the preceding wave, and the 5th group surpassed even home-reared American children from predominantly professional families in achieving the top steps on 5 of the 7 scales. Infants need not advance along all branches simultaneously; the kinds of experience encountered determine the branch along which advancement occurs. Theoretical implications were examined.