Half of Glasgow secondary schools are teaching at least three levels of the same subject to pupils in the same classroom, according to new figures.

A freedom of information request shows sixteen of the city’s 30 secondary schools use controversial multi-level classes - where National 4, National 5 and Higher pupils are taught together.

The request, by the Scottish Conservative Party, found in some schools up to 19 subjects were taught in multi-level classes.

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Subjects included English, chemistry, physics, biology, history, Spanish, French, modern studies and geography.

Multi-level teaching is not new, particularly in rural areas where the number of pupils in each school year can be low.

However, a recent Scottish Parliament inquiry heard the practice is becoming more commonplace, with concerns it impacts on the quality of teaching.

Liz Smith, the education spokeswoman for the Scottish Conservatives, said the Glasgow figures showed it was “abundantly clear” an increasing number of pupils were being taught in combined classes.

She said: “These statistics show that in half of Glasgow’s state secondaries, three lots of presentations are being taught in the same class and that, for many cases, this is in core subjects like maths, French and geography.

“Everyone accepts that there are some situations, most especially in small rural schools, where combined classes are essential, but it looks like multi-level teaching is fast becoming the norm.”

Ms Smith said teachers and education experts had warned the Scottish Government the issue was becoming more pronounced “placing additional pressure on teachers with the potential to undermine educational performance in our classrooms”.

However, Glasgow hit back arguing the figures were misleading because they did not reflect the small size of some of the classes involved.

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Maureen McKenna, the council’s executive director of education, also said the figures did not show the flexibility of the classes involved, with pupils sometimes changing qualification mid-term.

She said: “Wherever possible, schools timetable classes at one or two levels, but as the academic session progresses the level of qualification that pupils are presented for can change, which then gives the appearance that many different courses are being taught in the same class.

“The data also doesn’t show class sizes. For example, in some cases there were eight or nine pupils in each class.”

Ms McKenna said Glasgow schools were successfully raising attainment with the improvements recognised in national inspection reports.

She said: “Our teachers work exceptionally hard to maximise young people’s potential and are increasingly more successful with more young people than ever before achieving qualifications which are preparing them very well for life beyond school.”

Earlier this year, the Scottish Parliament heard “tri-level” classes could lead to lower standards, with the Royal Society of Edinburgh arguing it was a particular issue in the sciences.

He said: “Whilst courses may have similar titles, a National 4 in physics will be very different from a National 5, but quite often they will be taught together.”