Large representative samples of Negro and Mexican-American children from Kindergarten through 8th grade in largely de facto segregated schools were compared with white children in the same California school district on tests of mental abilities and scholastic achievement, personality inventories, and indices of socioeconomic and cultural disadvantage. It was found that when certain ability and background factors over which the schools have little or no influence are statistically controlled, there are no appreciable differences between the achievement of minority and majority pupils. Moreover, there was no evidence of a "cumulative deficit" from lower to higher grade levels between the mean achievements of minority and majority pupils when the differences were measured in standard deviation units. It is concluded that these schools do not cheat minority students in terms of conventional criteria. But it might be concluded that minority children are, in fact, cheated if it were shown that their ability patterns require different instructional approaches to optimize their scholastic learning. Marked differences, not only in overall level of ability but also in the pattern of abilities, were found among all three ethnic groups. (Author/GS)