Jacqui Miller, deputy general secretary of the Professional Association of Teachers, says: "People, particularly in secondary school, often choose the union they think will further their careers and therefore join the same one as their department head."
Her union, the smallest with 40,036 members is best known as the non-strike union and was the only union not to join the tests boycott. Ms Miller says: "Were are best known because of the no-strike rule and we did have a vocal religious group, but today I like to think we have earned a reputation for providing good services with a good network of field officers."
Barry Gandy, assistant secretary of the National Association of Schoolmasters Union of Women Teachers says half of all new new teachers are joining his union. The NASUWT traditionally recruits in the secondary sector, but the greatest growth area in recent years has been in primary schools.
He says: "When I go round the country talking to student teachers I tell them they should join the NASUWT because we will represent them the best, but even if they don't they should become a member of one of the unions. It is essential that teachers have legal protection, especially in these increasingly litigious days."
Parents, and pupils, are all suddenly getting wise to their "rights" and, according to Mr Gandy, some will sue at the drop of a hat.
"The law is useful for those who have money and that is why teachers should be protected by their union's lawyers and legal back-up team," says Mr Gandy. "Union lawyers can also protect you from employers - employment law is not enough. The teachers' pay and conditions document uses the word 'reasonably' at least 18 times. But what management may think reasonable and what you think is reasonable may not be the same thing."
The unions have all given publicity to cases of compensation they have won for members - in some cases more than Pounds 80,000 - for incidents, for example attacks or accidents, at school. The Association of Teachers and Lecturers has also distinguished itself by winning awards for members who have been given poor pensions advice.
The boycott of national curriculum testing which led to the Dearing review and slimming down of the curriculum has been a notable victory for the teacher unions. The NASUWT has also recently acted tough over the case of Richard Wilding, the Nottinghamshire schoolboy whose exclusion was overturned by an appeals panel. The union voted to strike after the turning down a deal with the local authority which would have meant the boy, who is said to be violent and disruptive, remaining in the school.
Teacher unions have had less effect in reducing job losses, but they argue they have kept compulsory redundancies down to a minimum. They believe they are still a powerful force in schools and many potential flashpoints never reach the news because deals have been brokered with the management.
Elaine Anderson, aged 27, joined all four unions when she was a student, but now she is teaching at Ridley High, Blythe, she has decided to stick with the NASUWT: "I was a bit put off by the NUT because of its militant reputation and the NASUWT was recommended by various staff I met during my teaching practice. "
But Elaine McNamee, 28, a supply teacher at Westgate Community College, Newcastle-upon-Tyne, says: "I joined the NUT because it is the biggest union and I thought it would be the most influential. I was also impressed by its regional service. There have been job losses at the school and the union has been very helpful and supportive."
The Association of Teachers and Lecturers recruits largely in secondary schools and has the largest membership from independent schools. While the independent sector is the least unionised, often it has the most difficult problems. "People often come to us when they have problems, but then it transpires they have signed an awful contract," says one field worker. It is also the only school teachers' union with negotiating rights with the further education employers.
Lynne Anderson, of Coleraine in Northern Ireland, will start her teaching practice in September, but she has already decided ATL is the union for her. She says: "I would not want to go on strike action and the ATL does not usually take this sort of action."
ATL: 0171 930 6441 NASUWT: 0121 453 6150 NUT: 0171 388 6191 PAT: 01332 372337 Educational Institute of Scotland (EIS): 0131 225 6244