resources, such as teachers or classroom units. Resource-based formulas include unit and personnel mechanisms in which distribution of funds is based on payment for specified resources, such as teachers, aides, or equipment. Under a percentage reimbursement system, the amount of state special education aid a district receives is directly based on its expenditures for the program. The variable block grant is used to describe funding approaches in which funding is determined in part by base year allocations, expenditures, and/or enrollment. Many states use separate funding mechanisms to target resources to specific populations or areas of policy concern such as extended school year services or specialized equipment. According to the CSEF report, a growing number of states have a separate funding stream that can be accessed by districts serving exceptionally "high-cost" special education students. Maintenance of effort The purpose of federal special education funding is to maintain or improve the quality of special education services. This purpose would be undercut if additional federal dollars were "supplanted" by merely reducing the level of state or local funding for special education. For this reason, like many other such programs, the federal law and regulations contain accounting guidelines, requiring "maintenance of effort." The statute says that federal funds provided to the local education agency "(i) Shall be used only to pay the excess cost of providing special education and related services to children with disabilities; (ii) Shall be used to supplement State, local and other Federal funds and not to supplant such funds; and (iii) Shall not be used ...to reduce the level of expenditures for the education of children with disabilities made by the local education agency from local funds below the level of those expenditures for the preceding fiscal year. 20 USC 1413 Regulations implementing this requirement begin with a test that seeks to assure that funds provided to a local education agency (LEA) under Part B of IDEA may not be used to reduce the level of expenditures for the education of children with disabilities made by the LEA from local funds below the level of those expenditures for the preceding fiscal year. Implementing this requirement fairly at the local level requires some exceptions Qualifying students for special education By federal law, no student is too disabled to qualify for a free, appropriate education. Whether it is useful and appropriate to attempt to educate the most severely disabled children, such as