Some guidance counsellors are being forced to give up space to make way for overcrowded classrooms, a teachers' association has warned.

Thousands of students are either starting or returning to school this week as summer draws to a close.

However, the Association of Secondary Teachers Ireland (ASTI) says overcrowding is among the problems impacting the well-being of students.

Speaking before the Oireachtas Education Committee today, ASTI Assistant General Secretary Moira Leydon observed: "We will find guidance counsellors telling us that they've had chaplains in schools or even the guidance counsellor themselves having to give up rooms where they will meet pupils on a one-to-one basis - simply because that room is now being commandeered for teaching purposes.

"When we talk about well-being and its priority in our curriculum, we need to look at the capacity of schools to actually give those supports."

Karen Jordan is the principal of St Catherine’s National School in Dublin 8.

She told the committee: "On the Department's own website, the average classroom size I think is about 80 square metres... our biggest is 66 square metres, so it completely falls short."

The number of secondary school students is expected to peak in 2025 so forward planning will be crucial.

A forward planner with the Planning Department says it is a complex issue and it cannot be generalised into a one-size fits all scenario.