They are feared by pupils and avoided by teachers. They are social hubs and bullies' hideouts. They regularly feature at the top of the children's commissioner's list of priorities.
But school toilets can also play an important psychological role in the lives of pupils, according to Nick Haslam, professor of psychology at the University of Melbourne in Australia.
In an article published in the journal The Psychologist, Haslam writes: "Psychologists have examined the psychobiology of eating, sleeping and sex at great length... We have examined how substances cross from outer to inner, but largely ignored traffic in the other direction."
Many of his findings are of particular relevance to teachers, who may be tempted to pass harsh judgement on pupils who ask to go to the toilet only minutes after break has ended.
In fact, excretion plays a role in a range of phobias, obsessions and compulsions. Paruresis, or intense fear of public urination, is common and often disabling. Many people are simply unable to relieve themselves during, for example, a busy break time. One paruresis sufferer cited by Haslam blacked out and crashed to the tiles from the sheer effort of trying to find relief in a public toilet.
Milder forms of what he terms "bashful bladder" are also widespread. Many people take longer to begin urinating when they know that someone is in the stall next to them. There are also deep-seated moral assumptions linked to the concept of holding it in until break time. Early psychologists believed that childhood incontinence ranked alongside arson and cruelty to animals as an early indicator of adult criminality.
Bladder control in childhood is still understood as a sign of wider self-control, albeit to a less pathological extent. And Haslam says that this attitude is not without scientific merit. When, in 2011, members of a test group were asked to drink five cups of water and then not permitted to urinate, they were then better able to resist unrelated temptations than their empty-bladdered counterparts.
(Methods of achieving continence, Haslam adds, have varied across history and cultures. In the Middle Ages, one cure for "pyssying in the bedde" was eating ground hedgehog. Among the Dahomeans of West Africa, repeat offenders had a live frog attached to their waist.)
But teachers should also be aware that many bladder problems can have a psychological dimension. Urinary retention, for example, is strongly associated with experience of physical or sexual abuse. Victims of abuse also tend to have higher-than-average levels of incontinence.
"In short, adversity, trauma and suffering commonly find bodily expression in disrupted excretory functions," Haslam says. "Excretion is related to an enormous range of psychological abnormalities."
Girls or women are often judged more harshly than boys or men for any lapses in bladder control. In a 2004 study, researchers found that women who excused themselves to use the toilet were judged more negatively than those who excused themselves to fetch some paper. The study showed that there was no such difference for men.
"Despite our enlightened modern attitudes to gender equality, women are still judged more severely for violations of (the) ideal of untaintedness than men," Haslam says.
Disgust is triggered by violations of rules of purity. And - even in the 21st century - girls and women are still expected to be inherently more pure than boys and men. "Women's excretion is more hidden, emotionally fraught and suppressed than men's," Haslam says.
Girls also tend to be more disgusted than boys by bodily waste, he adds. They are more censorious of flatulence, more concerned about concealing their smells and sounds during bathroom visits and more likely to wash their hands afterwards.
"Evidently, the bathroom is a space that is bound up with masculinity, femininity and the social codes that maintain them," Haslam explains.
Jodie + Tom 4eva no more
To the untrained eye, it may simply show that Dave luvs Kaz, or that Year 9 are wankerz. But toilet graffiti reveals much about the cultural differences between boys and girls, according to University of Melbourne psychologist Professor Nick Haslam.
In the 1950s, renowned sex researcher Alfred Kinsey was one of the first to enter the field of "latrinalia". He found more erotic content in gents' graffiti, while users of the ladies' room tended to focus on matters romantic.
Later research, meanwhile, has found that men's graffiti is "more scatological, insulting, prejudiced and image-based", Haslam says. Women tended either to offer toilet-wall advice, or to respond to earlier comments.
A 2003 study showed that men's graffiti was not only more libidinous but also more aggressive and excrement-focused, whereas women wrote at greater length and in a more conversational style. However, Haslam points out that later studies show that women "had achieved parity or superiority in quantity and explicitness".
He then reflects on the potential theories behind such findings. Psychoanalytic writers saw toilet graffiti as a form of "phallic expression", revealing an unconscious envy of women's capacity for childbirth. Semioticians argued that men were expressing political dominance, while women were responding to their subordination.
Social-identity theorists suggested that men and women polarised their behaviour in single-sex settings, so as to exaggerate their maleness or femaleness.
But Haslam says that latrinalia is in fact going into decline. "Arguably, in the internet age there is little point writing taboo thoughts on bathroom walls," he says. "Why scribble for a meagre one-at-a-time audience, when you can make...anonymous comments on a public discussion board?"
Psychology in the Bathroom by Nick Haslam is published by Palgrave Macmillan.
The article cited was published in the June issue of The Psychologist journal.