This booklet describes and evaluates an experimental home teaching program based on Piagetian developmental theory. The project was designed to stimulate infants' cognitive development and help mothers become more effective teachers of their children. Sixty-five infants, primarily from low socioeconomic status homes, were enrolled in the program at 3, 7, or 11 months of age, following administration of the Bayley Scales of Infant Development. Subjects were divided into three groups. Infants and mothers in the experimental group had weekly sessions (60-90 minutes each for a period of 16 months) with professional teachers experienced in early education or in working with parents and infants. Formally sequenced sets of informal infant play activities, individualized by the teacher to each mother child pair, were used in these sessions. The second group of mothers and infants had similar sessions conducted by college students and teacher aides rather than professionals. No formal curriculum was followed in these sessions; home visitors planned their activities autonomously. The first and second groups of infants were tested every four months along with a third group designated as controls. Experimental group children were found to perform at significantly higher levels on intelligence tests and showed greater linguistic skill than children from either of the other two groups. Other findings are reported. (BRT)