A number of hypotheses have been advanced to explain why black students lag behind whites in school achievement. In the 1950s and 1960s, an environmental hypothesis emerged which attributed the achievement gap to environment. Environmentalists at this point were divided between those who felt the family determined achievement and those who felt the school was responsible. The segregation hypothesis held that racial differences in academic success could be addressed by creating environments in which students from diverse groups were free to interact and learn together. Embodied in the "Brown" decision, this idea is presently under criticism for having failed to bring about satisfactory educational equality. Another environmental theory, based on a notion of cultural deprivation, argued that the family was the most important factor in determining school success. Compensatory education programs are based on this notion, which withstood attacks by the insupportable, discredited genetic theories of Jensen and Shockley. The Coleman Report of 1966 strengthened the deprivation hypothesis, and led to the widespread introduction of school busing, but this report was criticized by Christopher Jencks, who argued that most compensatory efforts are ineffective. In the late sixties, the cultural-difference theory was introduced. It is said that the culture of the school (school climate) must be reformed to make it more congruent with the diverse cultures of minority students. This development resulted in the concept of multi-ethnic education, which had its heyday in the 1970s. Today, multicultural education is challenged by economic cutbacks and ideological shifts. Finally, the recent effective schools hypothesis argues that schools do have a great impact on student achievement. Criteria for identifying effective schools have been advanced, and have served as a basis for various school improvement programs. In conclusion, it has been argued, any hypothesis chosen to guide the education of minorities must reflect the American values of equality, justice, and human dignity. (KH)