Successful early intervention models have used a variety of curricula. But relatively little research has been done that allows for a direct comparison of curricular effects. No single curriculum has been demonstrated to be superior to others (Bryant and Maxwell, 1997), but this may reflect the difficulty of separating out the effects of curriculum, program intensity, and teacher quality. However, research does indicate the importance for learning outcomes of having a planned, well-integrated curriculum (NRC, 2001b).

The intervention programs that have produced relatively large early effects, including the Abecedarian Project, the Brookline Early Education Project, Project CARE, the Milwaukee Project, the Infant Health and Development Program, and the Mobil Unit for Child Health, all provided health and social services, transportation, practical assistance with meeting pressing family needs, neurodevelopmental therapies when needed, and parent services and training in addition to quality educational programs for children.

The idea that individuals respond differently to any kind of “treatment” is pervasive in many domains, including child development, medical interventions, and education. Indeed, a key mark of progress is the extent to which differential responses (or person by treatment interaction) are understood and incorporated into the intervention. Many of the early intervention programs viewed children as either disadvantaged or not, and the treatment for the disadvantaged ones was a program or service that differed often by site, but for reasons unrelated to the characteristics of the individual children.

Several studies, however, suggest relevant dimensions for distinguishing among children in the intervention required and the response anticipated. The Infant Health and Development Program (1990) found that very low birthweight babies did not benefit as much from the intervention as their heavier counterparts. In a study of educational interventions for children with disabilities, Cole et al. (1993) found that children who were higher performing at program entry benefited more from direct instruction techniques, while lower-performing students benefited more from the mediated learning treatment. Findings from the Abecedarian Project showed the