For most of its history, Pennsylvania's public school system has consisted of three levels: the State level, the local school districts and an intermediate level. Until 1971, county superintendents supplied the structure between the State and local levels. In 1970, the General Assembly passed Act 102, creating a system of 29 intermediate units (IUs), which replaced the county superintendent offices as of July 1, 1971. The IUs were mandated to create a broad program of educational services to be offered to public and nonpublic schools, including curriculum development and instructional improvement services; educational planning services; instructional materials services; continuing professional education services; pupil personnel services; State and federal agency liaison services; and management services. Since the creation of the IUs, several amendments have expanded the mandated services that the IUs are required to provide to nonpublic schools. Presently, the IUs offer a large number of programs to school districts and nonpublic schools, in the areas of personnel training and curriculum development, technology, instructional materials, educational planning, pupil instruction and personnel services, special education, cooperative administration projects and statewide programs and services. The IUs have no independent taxing authority. Their major sources of revenues are State appropriations, governmental grants, sales of services, member school district contributions, student tuition, and income from investments. IU expenditures are made for employee salaries and benefits, purchases of professional and property services, and supplies and equipment.