It's often the toilet that is the giveaway. In some schools, it doubles as the disabled loo. In others, it's treated as an overspill to be used when the ladies' is busy. Some schools designate it as an extra storage room, for equipment waiting to be fixed. Still others don't have one at all.
The sad fate of the men's toilet is a sign of the dwindling male presence in primary schools: gradually falling out of use until it becomes nothing but a waste of valuable space, a neglected memorial to another era.
The shortage of men going into teaching might have reached worrying levels in secondary schools, but nowhere is it more acute than in primaries. Although a third of primary heads are men, fewer than one in eight classroom primary teachers are male. One in 10 primary schools in England has no male teachers.
Carl Pattison knows what it's like to be a member of this dying breed. Aside from his headteacher, Carl, 28, is the only man on the staff at Peafield Lane Primary in Mansfield, Nottinghamshire.
He's used to standing out, though. Now in his sixth year of teaching, he was one of just five men out of 60 on his PGCE course, and at his placement schools he was either the only male teacher or one of two.
Concern over the number of male primary teachers has focused on the lack of role models for boys. Carl takes his duties seriously in this area. He talks in class about his dislike of literacy lessons when he was at school, and reckons his choice of reading material - football magazines and autobiographies - can appeal to boys who are turned off by books.
"I've had parents say they're glad so-and-so has come to me because he needs a male teacher. I think all children should have a male teacher at some point. I don't think we're amazingly different; it's just we bring another dimension."
Outside the classroom, he admits to some of the perks of being one of this diminishing band. He has been mothered by female teachers and gets extra helpings from the kitchen staff, but then he is six foot tall. As payback, he is expected to sort out electrical equipment and do any heavy lifting.
A survey carried out for the Training and Development Agency for Schools (TDA) last year found that one in 12 boys aged eight to 11 had never been taught by a man. Although evidence on the value of male teachers as role models is inconclusive (see right), the survey found 48 per cent of boys believed male teachers set them a good example, 51 per cent said they behaved better for a male teacher and 42 per cent reckoned they worked harder.
Like Carl, Richard Tregear believes children respond in different ways to male and female teachers. The 26-year-old, one of three male teachers at Southdale Junior School in Ossett, West Yorkshire, says men may have a physical advantage in maintaining discipline through their height - Richard is six foot three - and lower voices that carry further. He adds that he never has any problems with the boys he takes for football. "Some kids are just crying out for a male role model who sets an example," he says.
He doesn't think the benefits of having more male teachers extend just to boys, however. "Girls can also respond well and I think any child who goes through primary school without having a male teacher is missing out. If nothing else, it might be a shock at secondary school when they'll almost certainly have male teachers."
One of three men at his primary school, Rob, a 31-year-old teaching in Lancashire who asked for his real name to be withheld, is regularly called on to break up playground fights and to appear at reception if parents become aggressive. It probably helps that, like Richard, he is six foot three. As well as extra-large servings in the canteen, he gets an indulgent smile when he walks across a newly-polished floor.
Rob isn't convinced that boys respond better to male teachers. He says that parents notice the teacher's gender more than the children, but he does believe men and women are different when it comes to behaviour management.
"There are fewer grey areas with men," he says. But this isn't necessarily a good thing. "Some children like the fact there are clear boundaries; some children think you don't listen to them."
Where the new gender balance makes a clear difference is in staffrooms. Carl says conversation revolves around family life and pregnancy; Rob knows football is taboo, and wryly recalls hearing a male colleague discussing Weight Watchers points and whether to avoid wearing stripes. "It's expected you'll talk in a female way," he says. "It's no place for a macho man." This also extends to playground duty. What female teachers might see as fighting, Rob sees as boys playing rough.
Chris Roynon, 37, the only male teacher out of 15 besides the head at Pensans Primary in Penzance, Cornwall, agrees. "Boys are boys and it is all right to have lots of energy and need to run it off," he says. "You need to know where to draw the line and I think some female colleagues find that harder to do."
Chris moved to Pensans after working in a school with two other male teachers and says the contrast between the staffrooms is marked. "I would rather I wasn't the only one. It would be good to talk about football and surfing again, but generally I don't bother because I feel no one is going to be interested."
More unsavoury than staffroom conversations about family life, there is also the stigma of being a male primary teacher in an age of heightened awareness of child abuse. Few men in primaries are not alert to the dangers.
"I've been in a room of 11-year-old girls changing for PE. I'm conscious of it, they're conscious of it, and I feel I shouldn't be there," says Chris. "Any primary teacher has to be careful, but it is worse for men."
Physical contact with children can be hard to avoid at the lower end of the school. While Carl, Richard, Rob and Chris all teach the upper end of school, Years 4, 5 and 6, Colin Marks is one of a small subset of the already small set of primary male teachers: he teaches infants.
Colin, 28, is in his sixth year of teaching and second year as key stage 1 team leader at Orton Wistow Primary in Peterborough. He reckons it's important for the children to see him as someone they can go to for reassurance, but sometimes he doesn't have much choice.
"I don't initiate a hug but if they come up to me I don't push them away, because they'd then see me as someone they would not approach," he says. "And if it happens in front of the parents it means they can see their children are comfortable with me."
The TDA is commissioning research into recruiting men into primary teaching, with the results expected by September. Colin believes the profession's female majority has become self-perpetuating.
"Just like nursing, primary teaching is seen as a female profession, and that is a factor when people choose their careers," he says. But stereotypes go farther. Colin is one of just two or three men when he goes on courses for primary teachers, but the balance shifts somewhat in favour of men when he's on courses for ICT co-ordinators.
Simon Eardley, Colin's headteacher at Orton Wistow, has made it a deliberate policy to distribute his male teachers - at three out of 11, he has a higher proportion than many - throughout the school. "It gives the children a chance to see that male and female staff can both be caring and help you sort out your problems," he says.
"It is important for children to see men doing roles that are traditionally done by women, such as the nurturing side of being a teacher or running art clubs."
With 18 years of teaching under his belt, Simon is philosophical about being part of a minority. "I don't think you can even consider being a male primary teacher without recognising you're going to be in a largely female environment. It goes with the territory," he says.
16: The percentage of male primary teachers and headteachers in England and Wales.
8: The percentage of male primary teachers and headteachers in Scotland.
12: The percentage of male classroom teachers in England.
11: The percentage of male classroom teachers in Wales. (Scottish figures not available).
Sources: Department for Children, Schools and Families; the Scottish Government; Welsh Assembly Government, 2006.
Country: percentage of primary teachers who are men (2005)
New Zealand: 17
United States: 11
Source: Organisation of Economic Co-operation and Development.
DO CHILDREN NEED MALE ROLE MODELS?
An assumption behind efforts to increase the number of men going into primary teaching is that boys need male role models. With more children coming from single parent families, and with that parent usually their mother, male authority figures can be conspicuous by their absence.
But research on the difference a male teacher can make is far from clear. A US study in 2006 did find that boys do better when taught by men; but a UK study the previous year suggested the teacher's gender made no difference to achievement.
The US research looked at the attainment of 25,000 pupils and found both boys and girls did 4 per cent better with a teacher of their own sex. When the teacher was male, boys were less likely to be seen as disruptive, but girls were less likely to look forward to the lesson.
A UK study carried out by the Curriculum, Evaluation and Management Centre at Durham University in 2005 drew the opposite conclusions, however. After analysing the data from 8,978 pupils in English primary schools, the researchers found no noticeable difference in achievement between children with a male or a female teacher.
The only link with the teacher's gender came when researchers asked about attitudes to school: pupils with a female teacher were more positive about school.
And what do the boys prefer? Again, it depends on who you ask. The TDA's survey last year found that 76 per cent of boys aged eight to 11 wanted their schools to have both male and female teachers. The previous year, researchers from London Metropolitan and Newcastle universities asked 300 children whether they preferred male or female teachers - the majority said they didn't care either way.
For their part, the TDA says its campaign is not purely about raising attainment, but about ensuring teachers are more representative of the population as a whole.