I'd bet that's the dollar amount the state or county spends per student, not including what the federal government contributes, which is considerable. I have a hard time believing that a privately run school, contained at the school itself and without the huge bureaucracy overhead, would cost more per student.
Have you ever been to a education district office? They're huge office buildings full of bureaucrats who...*shudder* this is bringing back a lot of unpleasant memories.
Let me see if I can dig up that article for you...