Advice sent out with the Association of Teachers and Lecturers' (ATL) magazine suggests that teachers should aim for the knee, solar plexus, elbow or little finger.
Teachers, it says, should first try to run away or shout and scream to deter the attacker, but "if all else fails, fight back - aim to `bash and dash'. Use only enough force to defend yourself."
The advice, the union says, is based on suggestions made by organisations such as the Suzy Lamplugh Trust.
A spokeswoman for the National Union of Teachers said: "To hit back can inflame the situation further and would be inappropriate with pupils and, with adults, it could lead to greater danger. It is far better to remove yourself.
"This is not advice that we would give. It is very difficult to make a rational decision in the heat of the moment."
David Hart, general secretary of the National Association of Head Teachers, said: "The ATL has given advice which could put teachers in a potentially difficult situation.
"Teachers who follow that advice could be in a difficult position in the eyes of the law and could find themselves being prosecuted."
Nigel de Gruchy, general secretary of the National Association of Schoolmasters Union of Women Teachers, said: "Bash and dash is rather rash. It could sometimes excite more violence and is very dangerous.
"If you are being confronted by a gang, to think that you can bash and dash out of that situation will make things worse.
"Each situation must be judged on its own merits. Teachers must think very carefully before offering a return of violence because it often makes the situation worse."
But a spokesman for the ATL said: "This advice has been prepared as a result of demands from our members. They are increasingly being left alone and vulnerable in teaching areas.
"We have taken advice from organisations such as the Suzy Lamplugh to try and help them defuse the situation and then fight back if all else fails."
The advice says that teachers should first try to run away to a busier part of the school, or shout and scream and set off their personal alarms.
Only if they fail to divert the attacker in these ways, should they fight back and then they should use only enough force to defend themselves.
The spokesman emphasised that the recommendations were designed to deal with intruders, not pupils and were directed at teachers who worked alone, for example, in temporary buildings at some distance from the main school.
Attacks on teachers are increasing. A recent survey commissioned by the Department for Education showed that teachers at one in five schools had been kicked or punched. At one in ten schools pupils were found to have brought weapons to school.
The main threat came from pupils, but attacks by intruders and by parents who were angry about the way their child had been treated were also a problem.
Last year, a teacher won damages of pounds 82,500 after being attacked and permanently disabled by a 10-year-old boy.
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