This paper presents and evaluates the broad results of pre-school intervention experiments and programs aimed at fostering the intellectual and social development of "disadvantaged" groups. Among the general findings discussed are (1) there is a "sensitive," or even "critical," period in child development, an age at which a child will be more susceptible to fostering; (2) a dominant share of intelligence develops during early childhood; (3) a gap in IQ between "advantaged" and "disadvantaged" groups exists before school entrance and widens thereafter; (4) "traditional" kindergartens do not protect disadvantaged children from lagging behind or failing in school; and (5) malnutrition or poor health have a marked effect on intellectual development. While studies have shown that IQ may be accelerated through pre-school programs, pre-school is not the "cure-all" it was anticipated to be. On the basis of the evidence available the author concludes that priority attention to pre-school intervention cannot be justified. Rather, priority should be given to educational support to the family unit. The most effective age group for such support is adolescents. An appendix extensively discusses conditions favorable for intervention during adolescence. (Author/RH)