Since the founding of Project Head Start in 1965, there has been intense public as well as academic debate about the effectiveness of early intervention programs in producing lasting gains in children's intellectual development. In the past few years, new evidence has accumulated at a rapid pace, and there are now over 100 major studies of longitudinal experiments and Head Start program evaluations. A series of longitudinal studies of early intervention experiments was begun in the 1960s. The children who participated in these programs are now past the third grade and old enough to give reliable responses to IQ and achievement tests. In addition, they have now been in school long enough to allow examination of their overall school performance. This volume includes reports which review both center and house-based early intervention programs. One of the papers presents preliminary findings from the Developmental Continuity Consortium which is pooling the data from 12 major longitudinal experiments. The authors cite evidence for late developing gains which seem permanent. These "sleeper effects" were not manifest in the scores of the same groups of children in the first few years of the postintervention period. In addition to IQ and achievement gains, there is also evidence for gains in emotional adjustment. Early intervention appears to have dramatic effects in the assignment of children to special education classes and on retention in grade, somehow enabling them to maintain their position in the classroom. In all, the papers describe 96 major studies which report positive impacts from early intervention programs.