The Illinois Constitution declares: "Education in public schools through the secondary level shall be free."

So why are public school parents in Illinois paying so many school fees?

The answer hinges on the definition of "free."

"Most state constitutions have some form of free-schools clause. It comes down to how the courts have interpreted it," said attorney Brooks Allen, director of education advocacy at the American Civil Liberties Union of Southern California.

Last year, his group sued the state of California on behalf of public school students required to pay what the ACLU described as "illegal" fees for materials including textbooks, workbooks and lab manuals. The case is pending as the group works with state lawmakers to prevent such