Baroness Warnock talked recently of the “disastrous” consequences of moving pupils out of special schools. The shadow education secretary, David Cameron, has issued an alert about what he calls the “inclusion police”.

With these sensible figures speaking out so intemperately, it’s no surprise that the Commons Education and Skills Select Committee has set up an inquiry into SEN .

Its remit is notionally about mainstream and special school provision, how statements are working, definitions of special needs, and the role of parents in decisions about children’s education. This is all important business, but no one imagines that the gaze of the committee will not drill down resolutely upon inclusion. I hope that the MPs will have the perspicacity to look beyond the visible horizon in its inquiry. I hope, in other words, that they will prefer evidence coming from broad-ranging research rather than narrow anecdote.

Baroness Warnock’s assertions stem, one gathers, from her daughter, a teacher, telling her just how hard it is dealing with autistic children in the mainstream. The Baroness has evidently been won over.

If Warnock changes her mind - if even the architect of inclusion retracts - something must surely be amiss. Well, one must remember that she wasn’t actually the architect of inclusion. She was the chair of a committee a quarter of a century ago whose recommendations for more integration were more or less inevitable, since the evidence available to it about the limited effectiveness of special schools was unequivocal. Moves to integration, not to mention the legislative drive against discrimination, were already well developed in North America and much of Europe.

But 25 years on, it is revealed that inclusion is difficult. Did anyone expect otherwise? Of course special schooling is more convenient for the education system. Children who make serious demands on teachers’ time are removed to special schools. The real issue - if we believe that inclusion is the right thing to do - is about how to make it work. Here, some brave decisions are needed from policy-makers about funding .

The international evidence shows that although special school pupils demand 15 times as much money as those in mainstream, this extra spending, seen in the round, has precious little, if any, effect on their progress. Many special schools do indeed appear to be doing excellent work, something that Mr Cameron has noticed in his own son’s case, but this is because they receive the lion’s share of resources for special needs.

For me, the way funding operates is the real issue for the committee and the one around which pivots all of its stated concerns about the availability of resources and raising standards. Much more money is spent on pupils in special schools, but the same money is rarely, if ever, made available for similar children who stay in the mainstream. Because of differing models of provision, funding is complex. One hopes that the committee will be advised on the appropriate questions to ask. But here is one simple question that MPs might consider asking a local authority executive responsible for special services: “Child X with behaviour difficulties is currently being sent to a residential special school at a cost of pound;200,000 per year. If you were to place that child, or were considering placing a child with equivalent difficulties, in the mainstream, would this amount - or even a tenth of it - be available to the mainstream school?”

The answer, of course, would be No (or at least a Sir Humphrey Appleby equivalent of No). Only a paltry additional amount, by comparison, would typically be available, perhaps for a teaching assistant’s time. It’s no wonder if inclusion is sometimes “disastrous” in Baroness Warnock’s terms: it’s not being funded properly. And that’s because the same numbers of places continue to be funded in expensive special schools - money isn’t following child.

As to definitions of special needs, MPs should be very wary. Remember what Baroness Warnock’s committee came up with 25 years ago. It defined a child with special educational needs as one with “a learning difficulty which calls for special education provision to be made for him”. This tautology (generated because definition was being attempted of something shapeless) is responsible for many of today’s problems, with anyone able to make a case out for a statement, and powerful lobby groups able to claim unfair shares of resources. Don’t try again, committee. You’ll end up with another piece of anodyne nonsense that will do more harm than good.

My advice to the Commons committee? Start with expectations for a non-segregated system (it is the 21st century, after all) and examine how money can follow child, perhaps looking to impose national differentiated banding wherein certain kinds of difficulty are grouped. This would enable children with equivalent difficulties in special and mainstream schools to be funded equally and thereby enable real progress to education that is not only inclusive but fair - to children, their parents and their teachers.

The writer is professor of education at the University of Birmingham