Contract out for support services. Private companies can operate cafeterias, provide school bus service, and maintain facilities and grounds more effectively and at a lower cost than school employees. These companies specialize in the services they perform and know how to deliver them efficiently. When they are local divisions of national firms, the can often use their bulk purchasing power to buy supplies and equipment at prices lower than what an individual school would have to pay. Don't custom-design schools.
New schools are usually custom-designed for a school board.
But except for vanity, there is no reason why school districts should insist on custom-designed buildings. Hire teachers in private practice. Some courses, such as advanced physics, calculus, and foreign languages, attract relatively small numbers of students and require highly paid teachers. Many schools hire full-time teachers capable of teaching these courses, and then have them spend much of their time teaching introductory classes or even managing study halls. Instead, schools can contract with teachers in private practice for just those hours that are actually needed.