Effective schools are those that successfully impart basic computation and communication skills plus some knowledge of the sciences, social sciences, and humanities. School effectiveness should be measured by looking at the total learning environment and outcomes for all students. This environment consists of three identifiable aspects--ideology, social structure, and instructional practices--that cannot be assessed independently, but only as an interdependent system. Previous research suggests that, while much of the difference in achievement outcomes among urban schools can be explained by the student body's social status and/or racial composition, differing characteristics of the schools themselves greatly contribute to these differences. Ideologically, the more a school expects from students generally, the more effective it will tend to be for all students. In terms of social structure, evidence suggests that the greater the differences in social status, and consequently in expectations, within the student body, the less effective the schools will be for the full range of students. Effective instructional practices seem to be those in which correct and clearly defined patterns of behavior are consistently reinforced. Although literature on effective schools is extensive, more research is needed to give tested, valid information about methods of improving school learning environments. (JBM)