Measuring the relation between participation in a preschool intervention program and long-term outcomes through the adolescent and adult years is a complex and highly speculative venture. On one hand, a hypothesized impact fuels public interest in the potential return on investment in the early childhood period. On the other hand, it raises expectations that may be unrealistically ambitious, tends to downplay the value of the enhanced well-being of children during the intervention itself, and fails to account for the significant impacts of intervening influences on development in middle childhood and early adolescence.
Central to the concept of long-term intervention effects is the notion of shifting developmental momentum prior to school entry in a manner that increases the likelihood that an otherwise vulnerable child will embark on a more positive pathway into middle childhood. Whether this favorable trajectory is sustained into the adolescent and later adult years obviously will depend on subsequent influences at multiple points along the life course. That is to say, significant medium-and long-term benefits of early childhood intervention may be viewed as a continuing developmental pathway that is contingent on a chain of positive effects that increase the probability of remaining on track.
Very few early childhood intervention programs have followed their sample into the adolescent and adult years. The most extensive data have been collected for graduates of the High/Scope Perry Preschool Program, which reveal statistically significant differences at age 27 favoring the intervention group over the controls in income and in rates of high school graduation, criminal arrests, and welfare participation, but no differences in teen pregnancy (Schweinhart et al., 1993). Intervention-control group differences in antisocial and criminal behavior also were reported for the Syracuse Family Development Research Program (Lally et al., 1988) and for the follow-up study of graduates of the Elmira Prenatal/Early Infancy Project (Olds et al., 1998a).
A variety of family-focused intervention models have been designed to improve the developmental trajectories of children at risk for problems as a result of environmental or biological vulnerability, as well as for those with diagnosed disabilities. The theory of change that guides such programs is grounded in the assumption that strengthened parent-child relationships and enhanced home environments promote positive outcomes for all young children across a broad range of functional domains (Guralnick, 1998; Sameroff and Fiese, 2000). Professional experience indicates that sensitiv-