ploy weaker methodologies, these studies indicate that public programs have been able to produce the same types of immediate and short-term effects (Barnett, 1995, 1998). Also, public preschool programs have successfully provided broader services to improve children’s nutrition and access to medical and dental services (Fosburg et al., 1984; Hale et al., 1990; Barnett and Brown, 2000).

The average size of the immediate effect of these preschool programs on cognitive development and achievement was about one-half of a standard deviation; effects in other domains tended to be slightly smaller (Barnett, 1998). Cross-study comparisons and a few planned within-study comparisons indicate that the magnitude of initial effects varies with the intensity and duration of the program (Ramey et al., 1985; Barnett and Camilli, in press; Wasik et al., 1990; St. Pierre et al., 1998). The programs with the largest initial effects on learning and development tended to be those that provided the greatest quantity of services (operating for more hours per year and continuing for more years) with high staff-to-child ratios (e.g., 1 to 3 for infants, 1 to 6 at ages 3 and 4) and highly qualified staff (Barnett and Camilli, in press; Frede, 1998).

There is some disagreement about the extent to which the effects of preschool education programs persist (Barnett, 1998; McKey et al., 1985; Woodhead, 1988; Haskins, 1989; Locurto, 1991; Spitz, 1986). In many studies—of both model programs developed by researchers and less intensive public programs—some of the estimated effects decline over time and are negligible several years after children leave the programs (see reviews by Barnett, 1998; White and Casto, 1985; McKey et al., 1985; Ramey et al., 1985). Some scholars have argued that fade-out occurs because of weaknesses in the schools that disadvantaged children attend after leaving the preschool programs (Lee and Loeb, 1995). Others (Herrnstein and Murray, 1994) have concluded that public programs like Head Start do not improve cognitive functioning, although more intensive and more costly preschool programs may do so. Close examination of the results from these studies suggests that there are long-term positive effects on children’s learning and subsequent school success, although the effects on IQ decline over time (Barnett, 1998; Barnett and Camilli, in press).

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