At the same time, it must be acknowledged that many of the hopeful claims of educators about ways to close the gap through better physical plants, smaller class sizes, more stringent education requirements for teachers, or greater racial, ethnic, and socioeconomic diversity, have not been supported by the data from rigorous evaluation research (although in the case of class size, the issue is really one of cost-effectiveness, since the benefits, though small, seem to be well-documented).