AT THE beginning of September the air changes. There's an uncomfortable dragging feeling in the pit of your stomach. Suddenly the leaves on the trees are auditioning for parts in a sepia-print poster. You feel strangely low though you may not even know why.

Let me remind you: it's called the back-to-school feeling.

Science has yet to pin down this phenomenon. Despite research into the winter blues, Seasonal Affective Disorder (SAD) has not been applied to September. There is no pill or light therapy. No one has measured the endorphin drop in people passing a "back to school" sign in Woolworths. Maybe it's because, like the common cold, it is everywhere and incurable.

The inertia of August makes the return to normality harder and your new school shirt all the stiffer against your neck. It doesn't matter how many years since you left.

"We learn in school that a good person is the one who is getting assignments in on time, who is making progress," says Ben Renshaw, a London-based "happiness therapist" who works with the NHS and privately. "If you measure your life against achievement, this is a stressful time of year."

According to psychologists, childhood forms a template of expectation that lasts a lifetime. As children it did not matter how unachieving we had been during the rest of the year - come September we moved up a class and a Startrite shoe size. Progress was imposed upon us.

Now we want progress to happen automatically but, with wage freezes, glass ceilings and a hundred other grown-up explanations, we are destined for disappointment.

"I eat more and start writing lists," says journalist Fiona Macdonald Smith, 31, about the start of September. "It is the impending sense of coming coldness and darkness, that somewhere you've forgotten something. I still feel like I've got an essay due which I've done nothing for.

"The older I get, the more the falling wrinkled leaves, the withering shoots, the nights growing longer, seem to be a personal metaphor for my poor decaying frame.

"Then I have remind myself that I'm not in school anymore and go and buy something nice (like support hosiery or anti-wrinkle cream)."

It is unfortunate that childhood has to be taken all at once. It would be useful if we could have a couple of the "Oh I've really got to change my life" years of the early forties stuck in between - say, 10 and 11, so that we had a more healthy perspective later. (It would certainly be refreshing if, as a belated gap year at 35, your job required no more from you than saying "here!" at 10 to nine and gave you 12 weeks holiday.)

Meanwhile, we require mental strength to overcome the Pavlovian need for annual progress. "We do live in cycles," says Renshaw. "September is seen as a new beginning. You can't fight it."

Beat back to school blues

1. "Do something nice for someone else," says Ben Renshaw. "Concentrate on their problems. This will take you away from your own neurosis."

2. Give yourself a treat. "Book a holiday. This is a good time to take up a new activity."

3. Make the most of it. Metaphorically sharpen your pencils. "Use that feeling of ambiguity," says Renshaw, "not to see if you are performing up to scratch but to check on whether your life is led by the things you really value."