As I write, Mike Tomlinson will be putting the finishing touches to his final report on the future of 14 to 19 education. There is no doubt that Mr Tomlinson is a skilful performer. Both as chief inspector of schools and as “Mr Fix-it”, following the A-level fiasco two years ago, he proved adept at walking the educational tightrope.

However, experience of all previous reviews of this sort suggests that general support (for example, for broad principles such as coherence and progression) wanes rapidly as the practical implications are spelled out.

Already some alarm bells are ringing. In July, the Confederation of British Industry expressed scepticism about the need for any sort of diploma to replace GCSEs and A-levels. Last month, Jonathan Ford, managing director of the National Assessment Agency, showed commendable independence in asserting that scrapping A-levels “would wreck education”. A recent survey of heads of some 1,300 independent schools - all members of the Girls’

Schools Association, the Headmasters’ and Headmistresses’ Conference, the Independent Schools Association and the Society of Headmasters and Headmistresses of Independent Schools - lends some weight to these concerns. Asked to rank their top five priorities for Tomlinson’s final report, they agreed the following order:

* Explaining how current qualifications will evolve into components of the diploma.

The plain truth is that GCSEs and A-levels will cease to exist. With 77.3 per cent of respondents citing anxieties about how the “re-engineering” of existing qualifications will actually happen, Tomlinson really needs to be explicit in his final report. Evidence from the independent sector suggests that the CBI and NAA are by no means lone voices on this issue.

lProviding further details of the content of the core of the diploma.

This second priority, cited by 61.9 per cent, suggests lingering doubts about what, exactly, young people will study from age 14. Tomlinson seems likely to recommend a minimum core of just three subjects (communication, mathematics and ICT), all of them reduced to a functional derivative of current GCSEs. Although, at key stage 4, students will be required to do more as part of their overall programme of study, the real danger is that the minimum becomes the norm. Yet in the independent sector, the normal expectation up to age 16 is likely to be the continuation of a broad core of full GCSEs in English, maths, a science, a modern language and a humanities or arts subject, plus some form of certification in ICT. One of the (unintended) outcomes of Tomlinson may therefore be a widening of the gap between the maintained and independent sectors. This would be both highly divisive and regrettable.

* Clarifying the volume of teaching, learning and assessment at each diploma level.

That 60.8 per cent cited this reflects the uncertainties left by the interim report. Details of what Tomlinson means for timetables, teaching and learning are now essential. In a diploma, made up of components rather than existing qualifications, a new and complex system of credit ratings for volume and level of learning will be needed. Although familiar to the further education sector, this is very alien to schools and the general public.

But one concern stands out above all others: assessment.

* Clarifying the precise assessment arrangements at each level.

This was highlighted as a priority by 60.2 per cent of respondents . For many, a real reduction in the overall assessment burden from 14 to 19 is more urgent than any other Tomlinson proposal. Specific priorities include a reduction in coursework at GCSE, AS and A2 (in that order) and fewer assessment units at A-level (four rather than six). The expectations are that such reforms should happen sooner, rather than later.

* Making clear that higher education fully supports the proposals.

Although only ranked fifth (at 58.6 per cent ), this remains the biggest challenge of all.

Ultimately it will be the response of university admission tutors that seals the diploma’s fate. We are told many tutors support proposals for an extended project (or dissertation) at advanced level and, by implication, the advanced diploma.

However, experience of the international baccalaureate suggests that, while the overall diploma may be important (and the “extras” it offers hugely prized), excellence in individual subject components is crucial. With all such achievements to be recorded on a new national “transcript”, many would question the need for the overall diploma itself.

In the end, while Tomlinson may advise, it will be higher education tutors who decide. If Mike Tomlinson is skilful in addressing these concerns, he may well stay upright where others before him have tripped.

But, as the old saying goes, the higher you climb, the harder you fall.

Unlike the interim report, this time there is no second chance and no safety net.

Let us hope that Tomlinson does, indeed, get the balance right when he goes public next month.

Geoff Lucas is secretary of the Headmasters’ and Headmistresses’ Conference