This study attempts to isolate variables which influence intelligence and achievement scores of disadvantaged black school children in the elementary school years. Based on a study of the mean changes in the IQ scores of third graders since they were in first grade, and of changes in the IQ and reading achievement scores of sixth graders since they were third graders, the report proposes that there are deleterious effects on the intellectual and academic achievement of black pupils. It is also proposed that these deleterious effects follow directly from their presence in a class where over a certain proportion of the student body is black. Social and psychological mechanisms contributory to the deleterious effects are explored. Socio-economic status along with inter-school mobility are also identified as two additional important variables. Tables giving test scores and results are included. (KG)