Ireland is heading for an oversupply of 38,000 teachers by 2036, according to a new Department of Education report.
In an extraordinary turnaround from the current shortages, a massive teacher surplus will start building in the next few years if nothing changes.
The report predicts an accumulated excess of 22,783 primary teachers by 2036, although the problem will be obvious by the mid-2020s.
Meanwhile, at post-primary level, the spare capacity in 2036 would be 15,249.
The projections are based primarily on the decline in pupil numbers over the period and maintaining the intake to teacher training programmes - and, therefore, graduates - at the same levels as today.
Other factors taken into account by the Teacher Supply Steering Group include estimates for teacher retirements, resignations, job-sharing and leave, such as career breaks.
Assumptions in the report are founded on current pupil-teacher ratios and it does not factor in the possibility of any improvements, as that is a Government matter.
But any reduction in Irish class sizes, particularly at primary level, which, apart from the UK, are the highest in the EU, would reduce the surplus.
The Irish National Teachers' Organisation (INTO), which has an ongoing campaign seeking smaller classes - with a current focus on schools in disadvantaged areas, is likely to seize on the findings to press its case.
The other area over which policy-makers have certain control is intake to teacher training, but here there is a need to ensure that any move to cut numbers would not damage the attractiveness of the profession.
There is also the added factor of a private provider in the market, Hibernia College, over which the State has no control.
In a foreword to the 'Developing a Teacher Demand and Supply Model for Ireland 2020-2036' report, Department of Education secretary general Seán Ó Foghlú describes it as a working document intended to form the basis for further discussion and consultation.
The challenge is to manage supply and demand, so as to ensure a pipeline of teachers, while avoiding an oversupply and large-scale teacher unemployment.
Teacher surpluses will become apparent at primary level from next year, as enrolments start falling after more than a decade of growth.
By 2029, the predicted excess is 15,752, up to 22,783 in 2036, when pupil numbers will be about 24pc lower than today.
Currently, there are about 37,000 primary teachers with 1,750 new graduates every year and, even allowing for retirements and resignations, there would only be a need for 6,967 of the projected 29,750 new graduates by 2036, unless class sizes are cut.
The picture is less straightforward at post-primary level, where there is the added complexity of ensuring there are enough teachers, but not too many, for different subjects.
Post-primary pupil numbers will rise by 40,000 to 2024, before decreasing by 75,000 to 2036.
There are about 29,700 teachers now and, based on current patterns, a further 31,430 would graduate over the same period, but, allowing for natural wastage, only 16,181 of these would be needed.