The recruitment of thousands of temporary teachers from overseas has helped to conceal a demographic time bomb that may leave the country desperately short of senior managers in 10 years time, a leading teacher employment analyst believes.
Professor Alistair Ross of London Metropolitan university says the use of foreign teachers has masked a key problem - the shortage of staff aged 35 to 44.
In England, 46 per cent of secondary teachers are aged 45 or more, as are 45 per cent of primary staff. But there is a relative dearth of 35 to 44-year-olds in both sectors. Only 24 per cent of secondary staff and 21 per cent of primary teachers are in this age category. The situation is just as bad in Wales and even more acute in Scotland.
Professor Ross believes these figures confirm that teacher retention efforts must be concentrated on 35 to 44-year-olds. He calculates that in 10 years time there will be only 42,200 veterans with more than 20 years experience to fill the 39,000 senior posts available.
Inevitably, some younger staff will plug the gaps, but Professor Ross says this may discourage their even younger colleagues who will see fewer possibilities for promotion as senior posts are filled by colleagues with a longer working life.
The outlook for primary schools is even bleaker as there will be 35,700 management posts to fill and only 36,300 long-serving staff to fill them.
"If the current level of experience is still required of primary heads and deputies in 2015, then two-thirds of all primary teachers over 45 will be heads, deputies or assistants.
"The message to teachers currently in their early 30s is if you want promotion in 10 years time, stick with it - a headship is guaranteed."
Cardiff university researchers have also been analysing teacher recruitment and have concluded that there is no supply crisis in Wales or most of England. "There are regional, occasional and subject-specific disparities, but there are now more teachers than ever before, while the number of pupils in schools in falling," they told the Edinburgh conference.
"Over the long term and for the immediate future the trend for pupil-teacher ratios is lower."
Beng Huat See, Stephen Gorard and Patrick White say that the major limitation on the supply of new teachers is neither the availability nor quality of applicants. It is the limits set by recruitment targets to initial teacher training and by the overall graduate population, especially in maths and science.
They add that schools and authorities in Wales should do everything in their power to make it easier for teachers trained elsewhere in the UK to find posts in Wales.
They also argue that, given the amount of cross-border traffic, teacher-training funding should not be split and devolved to England and Wales.