A well-aimed, well-founded campaign from the chalk face of the school system can put the chancellor under more pressure than any political assault. Jules White, a headteacher from West Sussex, has been coordinating a letter backed by up to 5,000 fellow heads of primary and secondary schools. They are all from counties that are at the lower end of the per-pupil funding league: they stretch from Cornwall to Cumbria, and on Tuesday they will call on the chancellor, to point out exactly what the Department for Education’s new national funding formula will mean in practice to their budgets. Conservative chancellors are often swift to dismiss such protest as producer interest, but if this is producer interest, it is what producers should be interested in – and what any parent would want their child’s teachers to be campaigning for: the resources available to the children that go to their schools. In the summer, more money was found to smooth the introduction of a scheme that, when it was shown to then prime minister David Cameron, was rejected instantly as an electoral disaster in the making. In fact this is a reform that is long overdue. It needs to work. For that reason alone getting it right should be high in Philip Hammond’s priorities, as he sweats through the final days of budget preparation.

The new national funding formula is meant to end the unintended unfairness of some schools getting very much more cash per pupil than other similar schools in a different part of England. It ends local councils’ power to use their own formula to fund schools, and it is meant to stop the postcode lottery. Yet because of the way the system tries to limit the losses any one school can be hit with, the new formula will still see some schools getting up to 60% less than a similar school in a better-funded borough. And many schools are already struggling financially because their budgets have not allowed for rises in costs like pensions and national insurance contributions, or inflation. Nor was there extra cash for a 1% teachers’ pay rise. The Institute for Fiscal Studies has estimated that schools are set to lose nearly £2bn by 2020.

The education secretary Justine Greening insists that per pupil funding is protected at least until 2019. That’s not how it feels in the classroom, where heads face battles to recruit and retain teachers, put off by larger class sizes, fewer teaching assistants and a shortage of basic resources like props for the school play. Ms Greening has tried to innovate, proposing schemes to offer rebates on student loans to entice teachers into shortage subjects like science and languages, and bursaries for maths teachers. But this is fiddling at the margins.

Mr Hammond is under instruction to produce a budget that, among the numerous other challenges and uncertainties that he faces, addresses the Tories’ new anxiety about intergenerational unfairness, in particular the cost of housing. But intergenerational unfairness goes far beyond the housing crisis, although that too is an urgent matter. Being fair to the next generation starts with ensuring that every child has the same chance of going to a good school and being taught by the best teachers. Schools can’t entirely make up for what happens at home. Some children will always find school easier than others. But every child should be taught in a school that is decently resourced so that it can meet the needs of the pupils who attend it. No amount of fiddling with the housing market will make up for the terrible unfairness embodied in an 18-year-old who has missed out on the qualifications, knowledge and skills they need to have their best chance of making a success of their life.