Energy is most school districts' second-biggest expenditure, behind salaries--a total of $6 billion a year for primary and secondary schools alone. The U.S. Department of Energy estimates that schools could save 25 percent or $1.5 billion of that if they had more efficient buildings.

Figure 15 Energy $mart Schools (ESS) Energy $mart Schools is a U.S. Department of Energy program aimed at making schools more energy-efficient.