"Herd immunity" is a phrase used to describe one way that viral epidemics spread. Say someone comes into a community with a new strain of flu, or Ebola. Because it's new, no one has resistance to it and it spreads easily throughout the group. But take another community, where most people have had their immunisation jab. The disease is often much more contained, because there are far fewer avenues of transmission. Herd immunity.
Of course, it isn't real immunity. You can still catch the disease if you're not resistant yourself, it's just that it's so hemmed in by immune potential hosts that it tends to travel less ambitiously. If you're susceptible to a bug but most of your community isn't, you're semi-protected by the umbrella of that group. Your umbrella still has holes, but it's better than a colander.
I'm reminded of herds when I think about classrooms and staffrooms, and not just because they both have bells and beef. Ideas are like viruses. They can be caught. They spread through intimate and airborne contact. They can make you sick. You can shake them in a few days. Every time someone sneezes in my classroom, someone coughs "Ebola!" under their breath (to be fair, it's usually me). In New York, rolling news heaves with scare coverage, as networks vie to see who can generate the most fear of a disease that hasn't yet killed a single US citizen. The sleep of reason produces monsters and in a society that still views contagious diseases in semi-medieval terms, fear spreads faster than any virus could.
And so in schools. On the day of the 7 July bombings in 2005, my classes shook with rage at the certain truth that the French had bombed London, although no one could verify where this idea had come from. In the absence of an informed majority, immune to falsehoods, the lie is halfway round the world before the truth can put its boots on.
And so in teaching. These days, in the salons of Twitter and education conferences, we chuckle at our near-ancestors' affection for the likes of Brain Gym. But the interesting question is how we fall for silly ideas in the first place. It's no good blaming research - although there is blame to be laid - because schools buy into such things.
Why? No herd immunity. Not enough people in schools who could smell the guano as it rained down upon them. For every timid voice that wondered "Is this shit?", a hundred people held up their hands and gasped: "Rain at last!"
That's one reason why we teach; so that children will be as informed as possible about the richness of human experience. So that even the ones who aren't are supported by the ones who are.
That's why teachers need to be as informed as possible in their subjects, their pedagogy, and the methods that inform both. So that the next time someone turns up with a car boot full of iPads or magic beans, or another crazy scheme that promises perfect results, enough of us can smell a rat and shut the door. It doesn't mean that everyone will be immune. Just enough of us.
Tom Bennett teaches at the Jo Richardson Community School in Essex and is director of the ResearchED conference