This paper presents a study of the relationship between scores on the Bayley measures of mental and motor development administered at 8 months of age and performance on measures of cognitive development and school achievement administered at ages 4, 5, 6, and 7. Also studied are changes in this relationship which occur when children with extreme scores on the infant measures are considered separately and changes which result when scores of children from differing socioeconomic status groups are compared. A review of literature related to infant test performance and later measures of intelligence and achievement is presented. Subjects for the present study were 1382 children who were participants in two previous longitudinal studies. In addition to Bayley infant scores and the subsequent cognitive and achievement measures, a measure of socioeconomic status was obtained for each child. Although moderate correlations were found between infant and outcome measures for the group as a whole, results more consistently indicated that low performance on the Infant Scales was associated with lowered performance on all of the intellectual and achievement measures, whereas high performance on the infant measures bore no relationship to performance on eight of the nine outcome measures. Results further indicated that SES was more clearly related to later performance for subjects with high infant scores than for subjects with low or middle range scores. (BD)