The worries about taking money away from the public schools are more valid: as I heard from many administrators whom I interviewed for my story about demography, shrinking school districts do not see their expenses decline as fast as their student numbers. Buildings still have to be heated, yards cleaned, and so forth. Because the student numbers decline across grades, they have to lose a lot of students before they can get rid of one teaching slot.

Still, if the voucher is for less than the current full funding of the children, I see no problem. And there's no question that public school budgets are bloated: top-heavy with administration, for starters. Too many city governments look at the schools first as a jobs program, second as a means for educating kids. Why shouldn't they? The mostly poor citizenry they serve aren't going to buy a house in the suburbs, and if they did, it would probably be a net fiscal plus for a city providing expensive services on a very thin tax base.

Vouchers, Democrats say, are no substitute for fixing the schools. This would be true if anyone had anything other than nice-sounding phrases with which to fix them. Giving money to failing urban school districts is like giving money to failing third-world economies; the entrenched interests siphon it off for their own uses. Teacher salaries go up, janitorial pensions get fatter, more administrators are hired. But the kids don't get any smarter.

Obama's plan to fix the schools: more money. More money for teachers, more teachers, more after school programs. Absent are any specifics about what the new teachers will do that is any different from what the current teachers are doing that isn't working. John McCain doesn't either, but at least he's planning to shake up the educational architecture that gets worse every year.

One of the central insights of economics is that exit matters. Markets don't do better, over the long run, because people in the private sector are smarter or well meaning. They do better because they can be fired. What's more, they frequently are: firms that don't satisfy their customers go away. Look at the businesses that people in America complain most about: cell phones, utilities, cable companies, health care. What they have in common is that the end consumers do not have meaningful right of exit--those companies have at least a temporary monopoly on their customers. Private sector firms can fail spectacularly, as many financial firms just did. But the important thing is that they fail. Schools that do to education what Bear Stearns did to mortgage bonds maybe get a stern talking to from the mayor, and in extraordinary circumstances, the principal may be fired. (Though this takes year). But the school itself keeps going no matter how bad a job it is doing.