A tidal wave is about to devastate primary and secondary schools, yet little has been done about it. The nature of the disaster and its effects are entirely predictable, but few serious preparations have been made to cope with it.

Here are a few more clues. It has happened before, in the 1970s and 1980s, so we ought to know how to deal with it. The graph on which it is based looks like a roller coaster. It will lead to school closures or mergers, and many teachers will lose their jobs. But the good news is that steps that can be taken to minimise the damage.

The impending disaster is, of course, falling school rolls. Crash! There goes a tumbling school enrolment. Bang! There goes another. Recent figures show that the birth rate has been dropping sharply. Every year the numbers of pupils entering primary schools will fall, and before too long secondary schools will also be affected. It is like a giant snowball, gathering momentum until it becomes an avalanche.

It is also an irrevocable and remorseless process, because there is nothing we can do to alter the size of the cohorts already born. A few children may come in from overseas, but others will emigrate, so that will hardly affect the situation. State schools may gain the occasional defector from the private sector, but some will move in the opposite direction.

Baby booms come in waves, with deep troughs in between, which is why the graph looks like a roller coaster. Immediately after the Second World War there was a high birth rate, as many families decided it was now safe to bring up a child, so in both 1946 and 1947 there were more than 800,000 births in England and Wales. The next peak was 18 years later when 875,000 children were born.

Falling school rolls follow the downward side of the graph, as large numbers of 16 to 18-year- olds leave schools and far fewer five-year-olds enter primaries. Each year the situation gets worse, until it bottoms out and the destructive process goes into reverse.

This year a cohort of 681,000 16- year-olds reached the top end of secondaries, but only 635,000 five-year-olds had been born in 1998 and were thus about to enter reception classes. Result: a fall of nearly 50,000 pupils. We already know the situation for 2006. An original 1990 cohort of about 706,000 will reach the age of 16, but only 594,000 babies, born in 2001, will enter primary schools. Result: another blow, the school population will fall again by more than 110,000.

In the 1970s and 1980s numbers fell by a third. First the primary sector was ripped to shreds. Village schools closed and smaller primaries in towns and cities shut or merged. Next the whirlwind hit secondary schools. They too were closed or fused, sometimes with catastrophic consequences.

Universities were not so badly affected, though more than a hundred colleges of education were closed or reorganised. This was because the birth rate in the highest two classes, from which more than three-quarters of students came, had remained the same. It was the near disappearance of the very large working-class family that had changed the landscape in schools and few of them, sadly, made it at that time to higher education.

There is a lot to be learned from last time. We cannot assume constant staffing ratios. Schools have to be overstaffed. When numbers fell by a third it was not possible to match this decline exactly with the number of teachers. It is difficult to have fractions of teachers in small primaries, nor can one simply dispense with certain subjects in secondaries, since the curriculum has to be protected.

Second, a great deal was gleaned about the problems of school closures and mergers. Close a school in a village that has lost its bus service and you kill the village as a place for families with children, other than the wealthy who send them off to boarding school. Squash two shrinking city schools together in an unthinking manner and mayhem ensues. The “host” school hates the “intruders”, while the newcomers feel alienated and resentful.

Third, there will be some areas that buck the trend, in both directions. In the 1970s there was a great deal of slum clearance and rehousing, so some schools lost well over the odds, maybe half or two-thirds of their pupils.

Other schools in the same city found their numbers actually increased, as new estates crammed with three and four bedroom houses were constructed on their doorstep. Exeter is an example of a city that is not going to experience the full force of falling rolls, because the Met Office has moved its headquarters from Bracknell and other firms have relocated there.

Fourth, although there is less time to prepare in infant schools, there is plenty of advance notice for junior and secondary schools, so no one need leave decisions until the last minute. During the last period of chaos, when the very expression “falling rolls” struck terror into the teaching profession, the Open University even put on courses telling people how to manage the problems.

One huge difficulty this time round, of course, is the changed role of local education authorities. Back in the 1970s LEAs were in the front line.

They were able to juggle budgets, move staff from one school to another, plan for a cluster of schools. Today, their powers diminished, solutions are much more in the hands of headteachers and governing bodies.

The good news, however, is that intelligent planning can turn adversity into advantage. In the past, considerable ingenuity was deployed to make sure that a potential catastrophe was at least mitigated and even converted into success. Some schools used the empty space to create a nursery. Other schools set up a resources centre, established smaller classes and special groups, or introduced daytime adult education or community activities.

If the first decade of the 21st century is not to repeat the errors of the 20th there are certain prerequisites. One important general message, straight from Corporal Jones of Dad’s Army, is not to panic. The problems of falling rolls are resolved by cool thinking, goodwill and imagination, not hasty schemes.

Let us capitalise on the experience in the profession where many senior members have witnessed the problem before. There is a vast pool of experience among the recently retired and the still employed that can be used to avoid a disaster. Step forward, ladies and gentlemen. Your country needs you as never before.