In addition to school vouchers, I think there are a couple really easy steps to take to improve education in this country.
It may be a civil liberties infraction, so I suppose that it may not work, but something along the lines of disciplining school age children who aren't in school during school hours would work wonders. The only problem is that it sets up a dangerous precedent. If an alternative could be found that would be less dangerous, that would work.
Another idea would allow children to get a driver's license earlier if they get good grades in school. Similarly, maybe you're only allowed to drink alcohol at 21 if you have a HS diploma, otherwise you have to wait til 23.