One of the hardest changes to achieve, it seems, is moving towards a broader range of studies at A-level. For at least 20 years, the traditional three-subject course has been criticised as being too narrow. Yet every attempt at reform has foundered.
When this Government took office, hopes were high that we would move towards some kind of baccalaureat; but ministers took fright under the impact of the standards lobby, and the British bac was stillborn.
Now the Government's timid attempt at a rethink has been rejected by the Joint Associations Curriculum Group - an influential coalition of independent and state school headteachers. They believe that the new plan for three A-levels at the current standard, plus two AS-levels in different subjects, is unworkable. Not only are there not enough hours in the week, they say, but encouraging every student to take five subjects would be very expensive.
Of course, cost has always been a problem. It was one of the factors underlying the invention of Advanced Supplementary levels back in the early 1980s, when the late Sir Keith Joseph was education secretary. His characteristically eccentric plan depended on the idea that, although an AS level should be at the same intellectual level as an A-level and should also take two years, it should only cover half the ground.
This solved the question of costs at a stroke. According to Sir Keith (who had but a hazy notion of the science of school timetabling), AS students could simply sit in on half the A-level lessons. This would create bigger teaching groups, but no extra expense.
In fact, AS has never really worked like this; many schools have used it as a half-way house on the way to an A-level, and put students in for the exam at the end of Year 12. The idea of using it to broaden their studies got lost fairly early on. Now it is to be revived.
In defending their proposals, ministers are right to point out that most 16-19s in continental Europe are taught for 30 hours a week - almost double the number of hours for a typical sixth-former. The headteachers, though, have come out fighting. Far from admitting that our young people might benefit from more teaching, they assert that time spent in private study prepares them more effectively for university.
It is true that British universities have an exceptionally high rate of successful graduation. But we also know that in some schools the high-flyers are taking four or even five full A-levels. How is this achieved?
Perhaps, by rejecting these admittedly disappointing proposals, the headteachers hope to persuade the Government to think again. But that's a dangerous game; virtually all their objections would be equally true of the baccalaureat approach. This too would be more demanding of students and teachers, and would involve more time and higher spending.
Instead, in the interests of a broader education for their pupils, heads should try to make this compromise work - and keep up the pressure for something better in the future.