Even within urban school districts, schools with high concentrations of low-income and minority students receive fewer instructional resources than others. And tracking systems exacerbate these inequalities by segregating many low-income and minority students within schools. In combination, these policies leave minority students with fewer and lower-quality books, curriculum materials, laboratories, and computers; significantly larger class sizes; less qualified and experienced teachers; and less access to high-quality curriculum. Many schools serving low-income and minority students do not even offer the math and science courses needed for college, and they provide lower-quality teaching in the classes they do offer. It all adds up.
Linda Darling-Hammond in Unequal Opportunity: Race and Education