ACCORDING to the Central Statistics Office, the drop in the number of primary pupils up to the year 2006 could range between 130,000 and 160,000 calculated from a baseline set in 1991. At second level, the decline is forecast to reach 94,000 to 97,000.

The trend in the longer term is expected to be similar. The number of births, which has fallen every year except one since 1980, is projected to persist under the CSO's low fertility assumption. The annual number of births could fall as low as 40,000 by the year 2006 - a 46 per cent decline from the peak level of over 74,000 births which occurred in 1980.

The high fertility assumption envisages a modest decrease in the total fertility rate to 2006, but low emigration could lead to a recovery from 1997 in the total number of births. Given the booming economy and the fall off in emigration, the latter assumption now looks the more likely.

Some experts feel that basing forecasts on the period 1980 to 1995 gives an exaggerated picture of the decline in births. They point out that the decline has tapered off in recent years, and the latest trends point to an imminent increase.

They also point out that Government social policy can have a huge impact on population trends. In France, for example, the Government managed to arrest a long term decline in the population through a calculated strategy of making generous payments to large families. Could the same policy prove necessary here?

But it isn't just a case of fewer children being born; an important explanation for the declining school population is that women are having children later, and they're having fewer of them. The increasing participation of women in the labour force, and the widespread availability and use of contraceptives are the major explanation for these trends.

The third major factor to be considered is the variation in the fall in different parts of the country. As the recent report from the commission shows, massive declines are forecast for some - mostly Western - counties.

So how many names are going to be wiped off school rollbooks?

According to the CSO, the fall in five to 12 year olds in the population between 1991 and 2006 will be at least 130,000, and possibly up to 160,000. Primary school numbers will drop by roughly the same amount.

The number of 13 to 18 year olds will also fall, by between 94,000 and 97,000. The corresponding drop in the school population will be about 90 per cent of this; not all teenagers attend school to Leaving Cert level.

Thus, the total decline in the school population is expected to be in the order of 250,000. That's equivalent to about 400 schools or more than 10,000 classes. Falls of this magnitude cannot be wished away, made vanish by political sleight of hand or hidden under the carpet.

Let's illustrate the situation by taking the example of one county - Mayo.

At present, there are 29 second level schools in the county, with total enrolments of about 8,000. Within a decade, numbers are projected to fall to about 3,900. This would give an average school size of about 130, if the various schools were the same size - which they are not.

But what second level school can survive with just 130 pupils on its rolls, or even 230? What kind of subject choice can it offer? How many football teams could it hope to field? What about remedial teachers, guidance counselling, administrative assistance?

But the problem isn't just confined to rural schools. It is estimated, for example, that there are 4,000 to 5,000 unfilled post primary places, in Dublin's north city. Notwithstanding the gentrification of inner suburbs, there is little prospect of a big increase in numbers over the coming years.

In fact, the only urban areas with a surfeit of pupils are along the fringes of Dublin, especially in the west of the county, and bordering areas in Meath, Kildare and Wicklow.

Irish schools are already small by international standards; 28 per cent of second level schools have under 300 pupils, compared to 18 per cent in Northern Ireland and 7 per cent in England, Scotland and Wales.

The greatest problems of over accommodation are likely to occur in regional towns, which tend to have at least three kinds of school - boys', girls' and vocational - drawing on an ever shrinking pool of students.

New Ross, Co Wexford, for example, is a small enough country town, but it currently boasts five schools. One has about 700 students enrolled, but most are languishing at the 300 mark.

Tuam, Co Galway, Portlaoise, Co Laois, Enniscorthy, Co Wexford, and Carlow are other towns which are likely to come under pressure as numbers continue to drop. Why, the Government will argue, should we subsidise multiple small schools in these areas when so many other areas are crying out for educational facilities?

The Department's projections are not accepted by the INTO, which maintains that the fall in the primary school population will not exceed 60,000.

Joe O'Toole, president of the INTO, whose nose for what's happening has in the past proved more accurate than computer predictions, also points out that a 25 per cent reduction in pupil numbers may not automatically translate into fewer teachers. If, for example, a school goes from 80 pupils to 60, it remains a three teacher school.