For teachers who happen to be one-dimensional caricatures, the decision of which union to join is an easy one.
Morning Star-reading socialist firebrands can join the National Union of Teachers, if they find enough time away from the picket-line to fill in an application form. Bearded sandal-wearers can discuss National Association of Schoolmasters Union of Women Teachers policy over a pint of real ale, once they have finished fulminating about the state of modern youth.
Meanwhile, those who prefer to spend their time breaking in sensible shoes at village fetes might be best joining the Association of Teachers and Lecturers. And those who are retired, who enjoy dressing in Victorian costume, or who believe that classroom assistants are a good thing, but only if they bark and go for walkies, join the Professional Association of Teachers.
The problem, of course, is that few teachers are one-dimensional caricatures. The majority are middle-of-the-road professionals who want to do a good job and to know that they will be protected in that job. And these teachers are faced with a choice of several unions with, at face value, very little difference between them.
The NUT, NASUWT and ATL each have more than 120,000 signed-up members. Each offers comprehensive legal cover and insurance in case of workplace injury, malicious allegations from pupils, or disagreements with employers. They have all influenced government policy over the years, by putting pressure on ministers for reform. It was the unions who first campaigned for teachers to have guaranteed planning and preparation time. The Government's behaviour task force, led by Alan Steer, was set up after NUT conference delegates called for a behaviour charter. And union threats of a Sats boycott led to a review of the curriculum and paved the way for the phasing out of key stage 1 tests.
Each union offers an array of free gifts, from the practical, such as pens or mugs, through to the oddly gimmicky. The NASUWT, for example, recently offered new members flashing mobile-phone holders and union yo-yos. The PAT distributes purple stress balls. The ATL gives out laser pointer-pens.
But, equally, union officials acknowledge that few professional decisions are made on the basis of whether a yo-yo or a bouncy ball offers more effective stress-relief.
The NUT, with more than 273,000 members, is easily the largest union.
Arthur Jarman, its assistant secretary, said: "We're the largest union, so we're the most representative. We only recruit qualified teachers, or those seeking qualification, so we focus on teachers' needs and nobody else's.
It's not a question of being left or right-wing. We represent a whole spectrum of opinions."
Meanwhile, Chris Keates, NASUWT general secretary, believes her union attracts the realists among teachers. She has more than 236,000 members.
Uniquely among classroom-teacher unions, these are drawn from all four countries in the UK. "My members are people who want a union that's pragmatic," she said. "But they're not shy of taking action where it's necessary. We're not characterised as being militant and hard-left. But we're teachers who want a union that will defend their interests."
NASUWT members are, however, often characterised as child-haters, quick to bemoan the rampant indiscipline in schools, and the lack of protection for teachers against this. "There's no doubt that the NASUWT stand on pupil indiscipline has recruited a lot of members," Ms Keates said. "We have a reputation for being able to put our finger on the issues that affect teachers. We don't represent pupils, parents or local authorities. Pupils don't pay subscriptions."
Teachers who find the NUT and NASUWT too hard-line are often drawn to the ATL. Mark Holding highlights the fact that his 122,813 members are drawn from all levels of the education profession, from nursery nurses to university lecturers. "We strive to represent members in their jobs and in their careers," he said. "We robustly represent them in terms of contractual changes, workload agreements and so on. But we also give advice when and how they need it. And we're serious about giving our members a true say in how their union represents them."
It was only in 1993 that the ATL changed its name from the Assistant Masters and Mistresses Association, an attachment to tradition, and its past rooted in grammar schools, that many believe reflects their conservatism.
"I can see how people might describe us as less militant than other unions," said Mr Holding. "People join us because they think, I don't want a strike to be imposed on me. We are robust and we do defend our members'
interests when we need to. It's a question of how we do it. We make clear what our position is. And we give people appropriate support and advice, to ensure they stay in teaching."
But the ATL will, occasionally, vote to take industrial action.
Alone among the unions in maintaining a no-strike policy is the PAT. Philip Parkin, its general secretary, says that many of the PAT's 34,104 members come from the disillusioned ranks of the other three unions. He himself was once NUT rep for his school. "A lot of people come to us mid-career," he said. "Many were members of other unions and were asked to take industrial action they didn't believe in. Our members join because they want a fourth emergency service. They want someone to help if something goes wrong."
But the PAT, with its ageing, more right-wing membership, tends to be seen as the eccentric uncle of the union family. This is compounded by its annual conferences, in which members have been known to put on Victorian music-hall performances, and vote for dogs to be recruited as classroom assistants. "It really gets to me, this eccentric label," said Mr Parkin.
"We have no more eccentric members than any other association. Motions intended to have a humorous bent have been picked up by the media. But we believe we are a mainstream association, serving education professionals."
All four unions offer a year's free membership for trainees and newly-qualified teachers. So some teachers postpone difficult decision-making by joining all four unions for a year, and then choose the one that best fits their needs.
Starr Green, 26, a modern languages NQT, took this Goldilocks approach while training at Leeds university. When she was unhappy with a school placement, she asked each one for advice. "One union just passed me around a bit, from one person who didn't know the answer to another," she said.
"But the NUT just gave me advice there and then. So I joined."
But there are increasing numbers of teachers for whom even joining a union at no cost is dauntingly proactive. Sara Bubb, of London university's institute of education, has observed a growing trend towards apathy. "I'm constantly annoyed by the number of NQTs who find themselves in trouble and then say, oh, but I'm not in a union," she said. "You need a real reason for not joining. It should be something teachers actively decide, rather than thinking: I'll get round to joining one day."
Faced with the reality of indifference, she suggests that few teachers are likely to choose their union based on close examination of their individual policies and political leanings. "New teachers normally join the majority union at the school they're working in," she said. "It does seem a bit sheep-like. But, in practice, if you're not in the majority union, it can feel uncomfortable when people go on strike.
"Some people think that, because you join a union, you have to agree with their every opinion on everything. That's not the case. Even if it's only to have personal protection against silly people making accusations, teachers need a union. Just join one."
NUT General secretary: Steve Sinnott
Number of members: 273,005
Represents: qualified teachers and heads
Cost: pound;130 a year; NQTs receive first term for free, and first and second years at half price:trainees join free for a year
General secretary: Chris Keates
Number of members: 236,005
Represents: qualified teachers, heads, classroom assistants
Cost: pound;136 a year; NQTs join free for first year in job and half-price for second year; trainees join free for a year
General secretary: Mary Bousted
Number of members: 122,813
Represents: anyone working in education, from early years through to higher education
Cost: pound;138 a year, but new members can join for pound;69; pound;38.75 for NQTs in first year of job; trainees join free for a year
General secretary: Philip Parkin
Number of members: 34,104
Represents: anyone working in early-years, school or further education
Cost: pound;145 a year; pound;50 a year for NQTs in first two years of job; trainees join free for a year