The idea that power lines and other forms of electromagnetic radiation such as microwave energy are health risks to human beings is not a new one. Then again the only real proponents of the idea are your usual crackpot pseudo-science groups with a marginal grasp of science. Powerwatch is one such pressure group that has leapt on board the issue with aplumb.
Naturally enough not a single of the many studies conducted has turned up any health concerns. The bottom line is simply this: there are two mechanisms by which some external radiation can affect us. Either by interfering with our central nervous systems by being active in low frequences or by ionising radiation possessing the the ability to create chemical changes in the the materials of our body. Electromagnetic radiation pretty much just doesn't interfer with the nervous system. A tiny tiny minority of people have sensitivity under certain specific and unusual circumstances. The subject has been examined a lot. On the second point, all electromagnetic radiation which is licensed for free transmission is of a firmly non-ionising frequency and hence the best it can ever do is heat you up a bit. Like a microwave oven.
There aren't any health risks. If there was, the sheer prevalence of all of these systems in our society would show up clear correlations. Consider how many people use mobile phones. Consider if the massive power transmitted directly next to the side of your head was a risk in even a tiny amount how this would translate to a large amount of observable health problems in heavy mobile phone uses. The correlation doesn't exist. All it does is heat the side of your head up almost imperceptively, and certainly well within the body to cool itself via normal means. These are the facts. They're concrete and well understood.
However where facts start to get to be a bit of a problem is when you combine it with the cocoon of illogical hysteria that surrounds the subject of children. Now it's one thing having ignorant hysterical parents demanding that Wi-Fi be removed from schools but it's quite another having the Professional Association of Teachers (a Union apparently) coming out and writing a letter to the Education secretary to demand a "full scientific investigation into the effects of wi-fi networks in schools".
This has all the hallmarks of your standard illogical non-scientific thinking. Apparently bad behavior in schools is up and Wi-Fi is the new thing in schools isn't it? So it must be due to that. One doesn't even know where to begin with this crap.
A Wi-Fi device transmits generally a fair whack less than 100mw of power in the microwave band. There's more power in the visible light knocking about in the room and that's actually more energetic than microwaves by a long shot. It's massively massively less power than mobile phones and of course it's not placed on the side of your head either. Any which way you examine it, there is no case to answer here.
Person gets headache. Must be Wi-Fi! There's this classics teacher that claims he's sensitive to Wi-Fi and can tell if it's on or off. He also claims he's developed sensitivity to other EM fields. Now that's actually possible. There are people who have an EM sensitivity generally to fairly powerful magnetic fields in low frequencies from 1Hz up to a couple kilohertz. Here's a study that gives some reproducable examples of some EM sensitive people and what conditions those were. This falls into the realms of low frequency signals interfering with the central nervous system, which we always knew was a possibility.
The bottom line is that there's basically infinitely more danger of mains cables with their substantial electromagnetic fields at low frequencies which there are reported cases of sensitivity to. Other culprits are CRT displays and flourescent lighting (particularly battery powered by an inverter) illiciting the kinds of reaction from people but that couldn't be more removed than Wi-Fi. There's no study showing any effects at all at microwave frequencies because they're far far too high to interfere with our central nervous system. The only real effect is that having being absorbed by common water molecules, microwave radiation dumps it's energy and heats up the absorbant material (such as us) which is how microwave ovens work. So this teacher that claims he can tell whether Wi-Fi is on or not? Bullshit.
There is some concern that things like Wi-Fi and mobile phones often tend to issue bursts of radiation in frequency patterns which are much much lower and that those bursts again fall into frequencies which can affect EM sensitive people. You're probably aware of that sound you get on any sound gear when a mobile phone checks in or you get a text. You're hearing the low frequency component of the pulsing of transmissions rather than the microwaves themselves. The microwaves can, and do, induce an electromagnetic field in conductors and that's what you're hearing. It is therefore conceivable that people with EM sensitivity could be sensitive to mobile phones due to the power.
However the actual low frequency component of the bursts is actually very low indeed. You've heard it right? That's not generally associated with EM sensitivity issues. If someone with EM sensitivity was sensitive to these bursts from mobile phones, they'd almost certainly face severe reactions from the similar frequency EM from mains cables and lighting on a constant basis.
Wi-Fi on the other hand is such a low power it doesn't have this kind of ability at all, that's why you've never heard your Wi-Fi inducing weird sounds on your amplifier. It's 10-100mw of power rather than several watts. Those are the facts and yet... if you want to be fully depressed on the subject, you can read the amusingly titled Dispelling the Wireless Myths on the Powerwatch braindrain site completely with some impressively sounding and massively flawed mathematics.
The problem is to most people Wi-Fi or radio in general is basically witchcraft they don't understand. That leaves itself open to any random correlation such as the fact it killed your cat because the same day you installed Wi-Fi the cat got run over.
Fortunately, in this case, about the only thing these crackpots can end up influencing is deployment of school networks so that they use wired networking instead. Which is hardly a disaster.