I was once teaching science to a class of seven-year-olds. The headteacher had told me the class was "not too bright" and so the limits to my knowledge of scientific topics would not be exposed.
"Science is about the world around us," I began in best child-centred manner, "so ask me any question you like about how things work." There was a split second of silence and then these apparently "not too bright" children opened fire: "Why are cars made of metal?" "Why does smoke come out of the back of a motor bike?" "Why does it snow?" "Why does a wagtail wag its tail?" It was nothing that a couple of lifetimes in the university library would not sort out. So I answered as best I could, and then to hell with the child-centred stuff. We did a topic on "energy", because that was the one I had lovingly prepared the previous night.
Explaining is a key professional skill. Every day teachers have to explain things to individuals, small groups, or a whole class. Research into children's opinions about teachers has consistently shown, since the 1930s, that the ability to explain clearly is the skill which they most value.
Children as young as three already have a pretty good idea which adults can explain something they don't understand. Once they are curious to know more about a topic or a problem they head straight for Aunty Mavis or Grandpa. Teenagers are in no doubt which of their teachers explain matters clearly and which can befog the simplest notion.
Over the years I have studied primary and secondary teachers explaining key concepts, abstract ideas, or undisputed facts. The best have an impressive repertoire of tactics and can choose just the right words and examples.
We can learn a lot about techniques of explaining from other communicators. Radio and television programmes often begin with an intriguing opener, such as: "And in a packed programme tonight, we'll be finding out how you too can become a millionaire; we'll be meeting the British underwater snooker champion; and we'll be showing you how to make a Porsche out of old socks; but first, the news." It is known as a "tease", because it not only sets the scene, but arouses your curiosity.
Capitalising on curiosity in this way is called an "advance organiser" in the literature on professional skills. It is a bit like the old tip given to university lecturers: "Tell them what you're going to tell them. Tell them. Tell them what you've told them", except that it is more intriguing. Also, explanations in school are likely to involve question and answer, demonstration and strategies other than socking it to them.
In one study primary teachers explained what "insects" were. One began, in a mysterious voice: "If I told you that in, say, a bucket of earth there were hundreds of them. They're in the air, they're even in ponds and rivers. There are millions of them in a tree. They live all over the world, except at the North and South poles." The whole class was agog, dying to yell out: "Insects!" as soon as he stopped for breath.
The language of explanations is crucial. Like teachers, doctors have to explain things to a variety of people. As in classrooms the explaining can often be a two-way process: the patient explains symptoms to the doctor, the doctor then explains causes and cures to the patient. The doctor must choose words carefully. Do you use the term "urinary tract", or say "waterworks"; "upper respiratory infection", or "common cold"; "low cholesterol diet", or "cut down on fatty foods"?
Secondary teachers may have to explain a term such as "inversely proportional" in science or maths lessons. The very phrase, in Boyle's Law, for example, may convince some 14 and 15-year-olds that physics is too mind-blowing for them, operating way up in the linguistic stratosphere. Yet the notion that "the more you have of this, the less you have of that" is not too hard to grasp. It is the language, not the concept, which kills the fainthearted.
Analogies can be helpful. An insect's eye was described by one teacher as being "like lots of marbles packed together in a plastic bag", and by another as "like lots of television screens put together side by side". Equally valuable are "not-analogies", ways of contrasting two things to show why they are not like each other. "Is a bird an insect?" is a clever opener, raising questions about body shape and number of legs.
New teachers learn a lot from explaining topics to their pupils. Undergraduates have usually learned the tricks of the examination trade - if you don't know something, try another question on the paper, or work your way round it. "Please misssir, what was the date of the Battle of Agincourt?" "Er, never mind Agincourt, let me tell you about the Battle of Hastings instead, much more interesting."
Not knowing your stuff, nor being prepared to check it out, doesn't wash with inquisitive children, for where would it end? "Brain surgery? Here's a scalpel, there's a brain, don't know too much about it myself." Master your facts and then become an expert at communicating them. The good thing about explaining is that, if you work at it, you can do it better and better throughout your life.
Ted Wragg is professor of education at the University of Exeter and a columnist on The TES. He also writes teaching tips on The Big Picture, a weekly teaching resource in The TES Friday magazine