is the marked heterogeneity of service formats. These include multiple variations and combinations of center-based and home-based models, guided by different blends of child-focused and family-focused philosophies. Significant differences in staffing configurations contribute additional variability, ranging from the highly professionalized services delivered by educators, developmental therapists, social workers, and nurses with advanced degrees to the highly personalized supports provided by community workers with limited formal education or training. Widely differing views on the definition of “early” provide yet another element of variability, ranging from preschool programs targeting 4-year-olds to prenatal services focused on expectant mothers. The breadth and the depth of these differences illustrate the diversity of the field of early childhood intervention (Guralnick, 1997; Shonkoff and Meisels, 2000; Zeanah, 2000). The extent of this heterogeneity underscores the challenges confronting policy development, service coordination, and evaluation research.
Closely related to the diversity of early childhood programs is the extent to which interventions are defined differently depending on the disciplinary lens through which they are viewed. Early intervention is a collection of service systems whose roots extend deeply into a variety of professional domains, including health, education, and social services (Meisels and Shonkoff, 2000). It is a field whose knowledge base has been shaped by a diversity of theoretical frameworks and scientific traditions, from the instruction-oriented approach of education (Bailey, 1997; Bruder, 1997; Wolery, 2000) to the psychodynamic approach of mental health services (Emde and Robinson, 2000; Greenspan, 1990; Lieberman et al., 2000; Osofsky and Fitzgerald, 2000), and from the conceptual models of developmental therapies (Harris, 1997; McLean and Cripe, 1997; Warren et al., 1993) to the randomized control trials of clinical medicine (Infant Health and Development Program, 1990; Palmer et al., 1988). At its best, early intervention embodies a rich and dynamic example of multidisciplinary collaboration. Less constructively, it can reflect narrow parochial interests that invest more energy in the protection of professional turf than in serving the best interests of children and families.
As its knowledge base has matured, the field of early childhood intervention has evolved from its original focus on children to a growing appreciation of the extent to which family, community, and broader societal factors affect child health and development. A natural outgrowth of this evolution is a recognition that individual programs are always delivered within a multilayered context, and that their effects are always moderated by the influences of more pervasive social, economic, and political forces. Thus, successful policies for children who live in adverse circumstances may have less to do with the impact of specific services and be more a matter of changing the larger environment in which the children are reared. This