development in the preschool years (Shonkoff et al., 2000; Zigler et al., 1996). These highly diverse initiatives have been included under the broad umbrella of what is called “early intervention.”
Early childhood intervention is more a concept than a specific program (Guralnick, 1998; Shonkoff and Meisels, 2000). Much of its diversity is related to differences in target groups—from the broad-based agendas of health promotion and disease prevention, early child care, and preschool education to the highly specialized challenges presented by developmental disabilities, economic hardship, family violence, and serious mental health problems, including child psychopathology, maternal depression, and parental substance abuse. Within this context, the diversity among and within subgroups is as great as that across the general population.
Generalizations about children with developmental disabilities are particularly problematic. As a distinct population, they represent a markedly heterogeneous group of individuals with a wide variety of impairments that differ in both their defining features and level of severity. These impairments may include various combinations of delayed or atypical skills in cognition, communication, motor performance, emotional reactivity, and social relatedness, among others. Specific disorders range from commonly recognized conditions (e.g., Down syndrome, cerebral palsy, spina bifida, and autism) to relatively rare and less known disorders (e.g., Rett syndrome, trisomy 13, and metachromatic leukodystrophy), with a large proportion of children whose conditions elude both a definitive diagnosis and a known cause (Guralnick, 1997; Shonkoff and Marshall, 2000).
Children with developmental problems that are presumed to be secondary to the influences of an adverse caregiving environment (e.g., poverty, family violence, parental mental illness) comprise a similarly heterogeneous population. In both circumstances (i.e., whether the vulnerability originates primarily in the biology of the child or the stresses in the environment), the cultural values of the family create a distinctive childrearing context that can present yet another set of challenges to the delivery of professional services in a highly pluralistic society (García Coll and Magnuson, 2000; Lewis, 2000). Nevertheless, all children deemed eligible for early intervention programs share a common characteristic—concern about their development or behavior, regardless of the cause, and a belief that formalized services can increase the probability of a more positive outcome.
Another major source of diversity among early childhood interventions