From what I've seen in my 20+ years experience in the classroom and with the work I've done with teachers across the state, here's what I think:
Vouchers to send poor kids to a great elementary school may be useful. But it'd need to be a huge voucher. Five grand ain't gonna cut it.
Even more useful would be to spend that money on a great Pre-K program. So many of those poor kids show up the first day of kindergarten and are already way behind.
Another good use of the money is an after school program for poor kids, where they learn social skills and have someone to help with homework--the things they aren't getting at home.
For these schools in low-income areas, find the best darn principals and teachers you can find and pay them very well. Leave them the hell alone and let them work their magic. (This means relaxing some of the demands the state puts on them, which should be done for all schools in my opinion). Give money for extra teacher assistants and make class sizes smaller.
Just my opinion, based on my experience.