The use of multi-level teaching is becoming increasingly controversial.

It is widely accepted the practice is not new and there are some circumstances where it is welcomed.

In rural schools with smaller class sizes, putting National 4, National 5 and Higher pupils in the same class is the only way to ensure they are able to study the subjects they want at the appropriate level.

The issue has come to the fore now because it appears to be increasing and routinely includes larger urban schools.

Recent figures show some 120 schools are teaching pupils at least three different qualifications at the same time. Eleven have pupils studying for four different exams.

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A study in 2016 by the Royal Society of Chemistry found 73 per cent of National 5 classes in the subject had pupils studying for other levels of qualification and 21 per cent of Higher courses were multi-level.

This has happened for two reasons. It has been a solution for some schools unable to attract enough subject specialists because of a national shortage of teachers. Multi-course teaching allows schools to maximise the impact of the staff they have.

The introduction of the Curriculum for Excellence (CfE) has also inadvertently contributed to its growth.

The first three years of CfE have been remodelled to give pupils a broader experience without the pressure of studying for exams.

What that means in practice is formal study of qualifications is put off for a year, resulting in a squeeze in S4 when schools try and offer as many options as possible in a shorter time frame. One way of ensuring schools can do that is multi-level teaching.

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But is it necessarily a bad thing? Some educationalists argue a good teacher with a small enough class is perfectly capable of making multi-level teaching a success, allowing pupils access to qualifications they would not otherwise have had the opportunity to study.

However, there is also a clamour of voices who believe multi-course teaching is undesirable and can even be damaging.

Teachers from the Educational Institute of Scotland union who took part in a survey on the issue thought it increased workload and contributed to rising stress and anxiety.

In terms of the impact on pupils, the survey found a majority of teachers thought it had a negative impact on motivation because of the difficulty pitching lessons in such a way as to engage all learners simultaneously.

The survey said: “Frequently commented upon was the difficulty that pupils experience in terms of the pace of lessons either being too fast or slow."

Asked about the issue in the Scottish Parliament Dr Alan Britton, a senior lecturer in education at Glasgow University, said: “The reality is most teachers, if given a choice ... wouldn’t want it.”