A recent study by the Manhattan Institute shows that school vouchers, now available to needy families of various kinds in Florida, do not just help those who get them - but improve education for those who don't as well.

As I learnt at the Heritage Foundation Resource Bank meeting in Miami last week, the Manhattan Institute shows that the performance of government-run schools increases when vouchers are introduced - or indeed, even just threatened. The same phenomenon has been noted with the municipal schools in Sweden, which also has a voucher-style education choice system. The supposed problem of: "What about those left behind?" just isn't a problem at all.

Manhattan also looked in detail at one of the Florida voucher plans, the McKay plan, a generous voucher arrangement to help disabled and special-needs kids access the education services they need in the private sector. The more disability they have, the bigger is the voucher.

Parents of these kids often had a hard time getting the services they need in the public sector. Theoretically a service plan would be drawn up for each disabled or special-needs child: but if those services are not adequately delivered, there is little parents can do about it. Only 30% in this traditional system say they have got the services they need.

But the Manhattan work shows that 80% of parents say they get all the services they need when they can shop around using the voucher. And they are pleased that class sizes have fallen, from 25 in the traditional system to just 12 in voucher arrangements, and that bullying is down too. All in all, some 90% of those in the voucher plan say they are happy with the system - compared with just 40% who are happy with the traditional system.