Thousands of science classes are being cancelled because of poor discipline, a lack of equipment and large classes, a survey shows.
Practical lessons were scrapped in more than three-quarters of schools surveyed by the Save British Science campaign.
More than half - 57 per cent - had cancelled practicals because of behaviour problems. Forty-nine per cent had cancelled classes because of a lack of suitable equipment and 46 per cent because the class was too large.
Almost three out of 10 practicals in the 67 English schools surveyed were scrapped because laboratory space was too small.
Peter Cotgreave, spokesman for the campaign, said: "We are very concerned.
If children are not experiencing practical science then they cannot be excited by it."
The study found that "perceptions of student behaviour was cited by teachers as one of the most significant deterrents for anyone considering a career in teaching.
"It may be that this has an even more significant impact on practical subjects like science."
Teachers also reported that poor facilities made it difficult to recruit, and hang on to, good staff.
Nine out of 10 felt that there were problems with methods of assessing practical skills.
They complained that there was too little time in the school day for science, and the curriculum involved "hoop-jumping" which limited the types of experiments they could offer.
A third said they were spending too much time teaching maths to make up gaps in pupils' learning.
Overall, 13 per cent of practical classes were cancelled for other reasons, including a shortage of support staff.
Teachers said they found it hard to recruit technicians because salaries were too low and jobs vulnerable to budget cuts. There was also a lack of suitable candidates.