Principals are concerned about a serious shortage of teachers qualified to cope with soaring numbers of students entering the second-level system.
The country's 720 second-level schools are already seeing a surge in enrolments as a consequence of the baby boom that started in the late 1990s. The additional pupils are working their way through primary level with enrolments up by about 10,000 a year – and by 2020 they will be transferring to post-primary.
National Association of Principals and Deputy Principals (NAPD) director Clive Byrne predicted a 15pc rise in new students starting second-level in six years' time.
The NAPD is concerned as to whether there will be the right balance between the numbers of teachers required, in relation to the subjects most in demand.
Mr Byrne said that, currently, there was no relevant data on the types of teachers who will be retiring over the next few years, and in particular, what subjects they taught.
He said the lack of data, coupled with the increased numbers of students, meant that there was a risk of a shortage of teachers trained to teach particular subjects.
"As 2020 draws closer it must be an immediate priority to begin planning for this challenge now," he said.
The Department of Education has committed to building new schools and recruiting the necessary number of teachers.
But Mr Byrne said it was "also essential" that there is the correct match between subjects taught at second level and having the right numbers of teachers to teach those subjects.
"For example, Ireland is becoming a leading player in the development of IT products and services. For this leading position to be sustained and grow, we need sufficient numbers of teachers to teach the STEM subjects of science, technology, engineering and maths at second level," he said.
The NAPD director also referred to plans for reform of the Junior Cycle to include new sources in subjects such as Chinese and computing, for which they needed "the right fit of qualified teachers".
However, Teaching Council director Tomas O Ruairc told the Irish Independent that the necessary planning had begun.
He said at the request of Education Minister Ruairi Quinn, the council was currently preparing advice on teacher supply.
"The overall goal of the process is to ensure a sufficient supply of teachers to meet demand.
"The outcome of the process should be a model that is sustainable and that will meet our needs into the future," he said.
Mr O Ruairc said in terms of subject- specific shortfalls, it was premature to comment.
He said it was a very complex issue and he hoped that the picture will be clearer towards the end of this year.
Under the new regime for teacher registration, teachers are required to declare their subjects, which will provide a clearer picture of the supply in given areas.
Mr Byrne said another area of concern was insufficient information and communications technology (ICT) resources in many schools, such as no Wi-Fi. This problem may intensify with increased student numbers.
Katherine Donnelly, Education Editor