Fears that unruly students will light gas taps or throw dangerous chemicals around mean experiments are being replaced by paper-based learning, they said.

They told the Save British Science pressure group that a few badly behaved youngsters were dictating the content of lessons.

Peter Cotgreave, the group’s director, said: “Experiments are inspirational and practical classes are an essential part of learning about science.” He said trying to teach without doing experiments was “like being told what a book was without actually reading one”.

But he added: “If you have a very disruptive pupil intent on causing trouble in a lesson involving acid or gas taps, it is not hard to envisage the horrors that might result.”

Dr Cotgreave said teachers feared that if they had to supervise one pupil continuously throughout an experiment, they would be unable to ensure well-behaved pupils were not inadvertently making mistakes.

Chemistry was the most obvious example, but he said all sciences could be affected. “There are biology experiments involving Bunsen burners and physics practicals using heavy weights,” he said.

The Association for Science Education is considering advice for members.

John Lawrence, deputy chief executive, said: “It only takes one child to cause a problem and that disrupts learning for everyone.”

He said classroom assistants might help by providing another pair of eyes in the room.

Save British Science has briefed MPs, who yesterday debated a report published last year by the House of Commons science and technology committee on 14-19 science education.

The report was highly critical of some aspects of secondary science. It said: “Practical work ... is a vital part of science education. Students should be given the opportunity to do exciting and varied experimental and investigative work.”

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