Why I'm proud of the pupil premium - The pupil premium was a key Lib Dem election pledge. We must prove we can deliver it

For Liberal Democrats, one of the silver linings in last week's necessarily tough spending review was the introduction of a £2.5bn "pupil premium" to help close the unacceptable gap between the life chances of advantaged and disadvantaged children. This was one of the four main pledges on which the Lib Dems fought the general election, and as a former schools spokesman for the party I was particularly pleased and proud to see the delivery of this promise. This shows that the coalition is determined to pursue an agenda of creating real opportunity for all, even as it has to grapple with the problem of the budget deficit.

Some people have tried to make mischief by claiming that the pupil premium is not additional money. This is nonsense. Without the pupil premium, I suspect that the budget for schools would have been based on a per pupil cash freeze for the period up to 2015. That would have meant a real cut in schools funding over the next few years. Instead, schools funding will rise by 0.1% (above inflation) each year until 2015 - that is a major achievement when the budgets of some departments are being cut by as much as a third. This is also a real-terms guarantee which the last Labour government was not able to make.

I know that Nick Clegg and Sarah Teather, as well as education secretary Michael Gove, have worked hard to ensure that schools were one of the real winners of the spending review. I am also grateful to my excellent Lib Dem successor as Treasury chief secretary - Danny Alexander - for helping to deliver the goods.

It would, however, be a terrible mistake to think that the main purpose of the pupil premium is to protect schools from cuts. Its real purpose is to help lift the educational performance of pupils from disadvantaged backgrounds, so closing the shameful gap in life chances in our country.

The pupil premium is designed to have two beneficial effects. First, because the extra money follows the child, it will ensure that deprivation funding is far better targeted than it is now. Second, the premium will deliver extra money to the schools with the highest level of challenge - giving them an opportunity to combat disadvantage. Too few schools facing real challenges currently have the money to make a difference, for example with more one-to-one tuition, a longer school day, holiday classes, or paying more to attract the best teachers.

Schools need to understand that they are being allocated the pupil premium to ensure that every child has a real chance to succeed. It is intolerable that so many young people, for example, still leave primary education with very poor reading, writing and maths skills.

So schools must not use the pupil premium to avoid making efficiency savings - they need to ensure that the pupil premium is used to do more for those who need the help most.

This government should not dictate to each school precisely how it should use the pupil premium - the coalition is moving away from Labour's obsession with micro-management. Schools will be held to account for their outcomes, and not for following some government mandated method.

But we should develop a clear framework of accountability, including through Ofsted, to ensure that the pupil premium is being used both effectively and for its purpose. There should be clear advice and support available to schools so that best practice in using the premium can be spread. Schools which fail to use the premium to close the performance gap, or who use the money ineffectively, must be held to account.

Proving that the pupil premium can deliver is crucial if we are to develop this policy in the future. By 2014/15 the government will be spending £2.5bn on the premium, but I would personally like to see funding in the next parliament grow towards £5bn per year, to cover more pupils and to ensure that schools have the resources to match the very tough challenges. We therefore need to revisit this issue later in this parliament, by which time the public finances should be in much better shape. But if we are to persuade the chancellor of the exchequer to continue to grow this programme further, schools now need to rise to the challenge which has been set.