Predicting teacher supply is often a matter of guessing whether it will be "feast" or "famine". There seems to be no happy medium.
Just two years ago, schools were in the midst of the biggest staffing crisis in years. In the spring term of 2001, schools, both state and independent, placed more than 4,300 adverts for mathematics teachers. That summer, they advertised another 2,000 maths posts.
With poor responses, some schools may have placed the same advert several times. But, even so, this was almost double the number of maths vacancies advertised between January and July 1999.
The media coverage that the teacher shortage of 2001 attracted led the Department for Education and Skills to set up a special unit to advise local education authorities on how to handle staffing problems. It also prompted an influx of teachers from overseas, as supply agencies and local authorities went shopping around the globe.
Now, just two years later, as many schools start to worry about their budgets again, there has been a sharp fall in the number of adverts for maths teachers. The autumn adverts tally was up on the previous year, but the spring term looks set to produce the lowest number for three years - unless there is a sharp increase in the last two weeks of April.
There are still far more posts for maths teachers than there are trainees, so maths students should have no problem finding teaching posts this summer. However, some of the overseas teachers who return home may not be replaced by another overseas-trained teacher. The slowdown in the job market will also be good news for teachers press-ganged into teaching maths "because there was no one else to do it". They might even be replaced by a trained mathematician.
What the future holds will depend upon the interplay of three conflicting forces: future funding levels, rising numbers of retirements and falling pupil numbers. Forecasting teacher supply is still very much a voyage of discovery: all too often it seems to be on uncharted waters.
John Howson is a visiting professor at Oxford Brookes University and a director of Education Data Surveys