When cobbling together the landmark No Child Left Behind Act in 2001, Congress quietly tacked on an unusual provision that says the law does not require states or school districts "to spend any funds or incur any costs not paid for under this act."

Little noticed at the time and lifted directly from an earlier version of the law enacted in 1994, the clause was originally pushed by Republican legislators wary of federal intrusion into schools by the Democratic administration of President Bill Clinton.