This study examines effectiveness of preschool and family intervention in prevention of cultural-familial retardation. It attempts to resolve part of the complex of influences on early intellectual development in those born into seriously disadvantaged environments that could account for the increased risk for certain children to be identified as mentally retarded. Development of 17 subjects from infancy through age 15 is charted in terms of intellectual and related measurements, alongside 18 controls. Chapters include "Introduction to the Problem"; "The Course of Early Intellectual Development"; "Design and Method"; "Assessment of Intellectual Development"; "Learning and Performance"; "Assessment of Language Development"; "Mother-Child Interaction"; "Follow-up Assessment of Development"; "Analysis of the Children's Performance in School"; "Family Risk and Child's Intellectual Development"; "The Children and Their Families"; and an epilogue discussing the role of maternal mediation and methodological factors. (PB)