NUT policy is that group sizes for all practical work, including science laboratory lessons, should be no greater than 20 for all timetable groups up to KS4. We copy below further advice received from the Association for Science Education, which will be useful in arguing the case for smaller science groups in schools. If your arguments are unsuccessful, please contact the Suffolk NUT for assistance.
"The optimum number in a Science class will depend upon the age, ability and degree of responsibility of the pupils, the type of work being attempted, the nature of the laboratory and the experience of the teacher. Thus for some classes, three might be too many, while a lecture can be delivered as safely to 30 as to 15 pupils.
A survey in England and Wales, published in 1994, suggested average class sizes were 23.2 at KS3 and 20.8 at KS4. ASE policy is that group sizes should be limited to a maximum of 20 at Key Stages 3 and 4, and of 14 for post-16 work.
There is no direct evidence that more accidents occur in larger classes, possibly because teachers are more inclined to limit practical work in such situations, with the result that pupils' education suffers. There are particular difficulties in adequately supervising open-ended projects and investigative work. Laboratory size is also an important factor. Cost limitations mean that most new laboratories are likely to have an area of about 80-85 m2.
A useful rule of thumb suggests there should be 2m2 of "free floor area" for each 11 year old, rising to 3m2 for 16-yr olds. In addition, each pupil needs a minimum of about 0.36m2 of work surface. Distances between work spaces are also important.
If, in a teacher's professional judgement, a class is too large or a laboratory too cramped, to attempt a particular practical activity safely, then other strategies need to be considered. These might include abandoning the activity, having only part of the class doing practical work at any one time, adopting pupil-assisted teacher demonstrations, swapping rooms, etc. Some strategies may affect the teacher's ability to deliver the National Curriculum properly. It the problem persists, a class teacher should consult the head of department; it may be necessary to inform the headteacher in writing and to involve a teacher's trade union."
Re-published by Suffolk NUT