One hundred seventy-four preterm survivors of hyaline membrane disease, born 1961 through 1971, were followed up for at least six years with serial psychological and neurological evaluations. This relatively mature population had a mean birth weight of 2,133 g and gestational age of 34.6 weeks. All children had consecutive preschool and school age psychological tests. The mean preschool test score was 91 (SD = 13) and the mean school age score was 101 (SD = 16). The ten-point difference between the mean preschool and school age test scores was significant. Perinatal variables and indexes of disease severity did not correlate with test scores. Higher test scores were correlated with higher paternal educational and employment levels. Improving test scores by school age may be due to test instruments that measure different cognitive skills and/or the diminishing effects of prematurity.