There is a new zero-tolerance approach sweeping schools, but it has nothing to do with behaviour. Instead, it is wheat that is being shown the red card as dozens of teachers on The TES online staffroom (www.tes.co.uk) insist that it is responsible for making them feel bloated, tired and generally unwell.
But research indicates that they may be denying themselves foods such as bread, cake, pasta and cereal for no good reason.
Although 20 per cent of people perceive themselves as having an intolerance or allergy to food, it is estimated that true food intolerance affects less than 2 per cent of adults. In terms of allergy, it is less than 1 per cent.
Part of the problem is a confusion over definitions, according to Claire Williamson, a nutrition scientist at the British Nutrition Foundation (BNF). While allergies are a physiological reaction by the body's immune system that can be medically tested, intolerances cause more general discomfort and are much harder for us to identify.
Despite this, spurred on by media attention and celebrity fad diets, self-diagnosis is spiralling. A survey by the Grain Information Service in 2002 found that more than 40 per cent of women eliminated specific foods from their diet over the past five years, to the disapproval of 87 per cent of their GPs.
"A lot of people think they have an allergy or intolerance to a certain type of food when they haven't," says Claire. "If you feel better when you cut wheat out of your diet, for example, it's hard to know if it's the wheat that is responsible or the fact that you are consuming less sugar in a pastry."
This will not stop some people avoiding all wheat, possibly to the detriment of crucial nutrients. One teacher on The TES forums reports: "Recently, I did an elimination detox diet and found that I have a wheat intolerance. Since then, I have no symptoms when I don't eat gluten, but they come back with a vengeance when I do."
Claire warns against using internet tests or cutting out wheat or dairy without first seeing a doctor or dietician. They can provide a proper diagnosis and introduce a controlled elimination diet over the course of two weeks, before gradually reintroducing the food.
Nicky Palmer, a modern languages teacher in Leeds, is certain that she has a milk intolerance following hospital tests.
Having suffered from bulimia for 20 years, her stomach acids are disturbed, which results in involuntary vomiting after eating dairy food.
"I can take milk in tea, but that's about it," she says. "I don't eat school food as it disagrees with my digestive system and then makes me vomit. I also avoid school social events that involve food, meaning that people tend to think I'm a bit unsociable."
Nicky's diet results in low energy levels, which she counters by drinking fizzy caffeine drinks, but her experience illustrates just what a formidable task elimination diets can be. Wheat is such a staple part of western food, it can be hard to avoid, the BNF confirms.
It is a ubiquitous thickener or extender in "non-obvious" foods such as soups, sauces, sausages and pate; even beers and malt contain a protein present in wheat and so should be avoided by truly intolerant patients.
Removing all the possible triggers can lead to people missing out nutritionally, socially and in terms of taste, the BNF says.
"A lot of talk about wheat intolerances is a popular myth," says Claire. "A true allergic reaction to wheat is coeliac disease (a permanent and potentially serious gluten allergy) and you would certainly know about that. Instead, so many people have a hunch and lose out on important nutrients and calories while still inadvertently eating wheat."