A study was conducted to determine if the observed changes in Head Start children were related to the practice effects inherent in a test-retest situation. The "control" group consisted of 64 children who had been eligible for a Head Start program. They roughly matched a group of Head Start (HS) children in IQ scores, age, and socioeconomic level. On two occasions, with about 83 days between testings, the Stanford-Binet and Preschool Inventory tests were administered to the control group. The same tests had been administered to the HS group in a study by Temp and Anderson in 1967. The control group did not have a statistical gain in Stanford-Binet IQ scores, whereas the HS group did have. On the Preschool Inventory both groups showed statistically significant gains in most instances. The results support the position that the gains in the Stanford-Binet IQ scores were atrributable to Head Start practices and that the increases in the Preschool Inventory scores were attributable to maturation. The Preschool Inventory should be scored to allow for maturational differences. Tabulated data are included. (JS)