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This article reviews primary research studies investigating the efficacy of early intervention with handicapped preschoolers. Meta-analysis techniques were employed to integrate statistically the findings from 74 studies. Findings indicate that: (a) early intervention with handicapped populations produces a positive sizeable effect size; (b) longer, more intense programs are associated with efficacy; and (c) little support was found for commonly held beliefs about early intervention, such as the importance of age at start and the degree of parental involvement. Implications for future research are discussed.
Casto et al. (Sat,) studied this question.