To see ourselves as others see us. Isn't that supposed to be good for the soul? Or maybe just bad for the ego.
But what the heck? I decide to give it a go anyway: to cross the line and see what life is like on the other side of the teacher's desk. After some delicate negotiations, I find a sixth-form college, on the outskirts of London, prepared to let me in through the door and pretend to be 17 again.
So what is life like as a teenage student? It's tough, that's what it is.
They throw so many things at you all at once. It's 10 to 9 in the morning and I've just got myself settled in and it starts. Answer your name. Why are you late? Sign up for parents' evening. Fill in this, fill in that.
Then there's the homework to be delivered up. Or not, as in my case. I slide a little further under the desk, hoping not to be noticed. There's a lot of "hoping not to be noticed" in this student business I am to find out.
My new classmates are curious about this unexplained addition to their numbers. They look at me with that particular adolescent look - half grin, half snarl -that says "'Oo is this old git?" Heaven forefend, but they probably think I'm an inspector!
The class is English literature, my subject, so I should be at home. The trouble is, I'm not. I packed in teaching A-levels just as the AS and A2 system arrived back in 2000, and the first thing I notice is how much it has changed since then. We are performing a textual autopsy on John Donne's poem, The Flea. The poem is about sex - the same old story, he says yes, she says no -but there's nothing sexy about the way we are having to slice it up. This is no fault of the teacher. There's an exam to be passed, as she reminds us more than once, and the board lays down very precisely, very mechanistically, how our analysis should proceed.
So, for 15 or 20 minutes we play spot the structure, apprehend the alliteration, count the conceits. They are good at it, these teenagers, albeit that they get a little help from sources not readily available when I was sitting in A-level classes for real: when Ambreen comes up with a "syntactic parallelism" she tells us proudly, "I got it off the internet".
They don't seem to mind either that, as soon as they've finished their GCSEs, here they are again preparing for yet another imminent exam. When you think about it, having begun their Sats virtually as they were teething, they must be the most-examined generation ever.
Although I try hard not to, I find my eyes straying towards the clock. Now that's one thing that really is different on this side of the divide. As a teacher you've never got enough time. You never notice the clock except to curse it. Tick, tock, blink and you've missed it. The lesson's over and still you're only half way through your lesson plan.
Meanwhile, things have moved on. We've done Donne and now it's Marlowe's turn to be fed into AQA's poetic mincing machine: "Come live with me and be my love..." drifts out into the classroom. Farouk (one of the students) is taking the lead on this one. Marlowe's vision, he tells us, is an idyllic myth: "The couple are trying to get back to Eden," he says. Our "Myth" is clearly impressed by this analysis, but suspicious about its origins. Where did you get that from? she asks. "The internet," choruses the class.
Class ends. I leap up and lug my imaginary back-pack of books into a geography lesson. As in the first class, I am given the once-over by my new classmates. You can see them peering at my wrinkles: 'This boy's had a hard life,' they're thinking.
Geography is more relaxed than English. There's fewer of them, and they know one another better. The class are working on weather systems, and once again the internet is to the fore, with the teacher beaming an image direct from cyberspace up onto the screen at the front. When one of the boys gets an answer wrong, a couple of the girls are on hand to put the verbal boot in. "Look how he has to list all the months just to get the right one," one of them says. It's good-natured enough, but it reminds me how much taking the piss is part of the learning process.
Before I've even thought of looking for the clock, I am whisked out of geography and into another literature class. My heart lifts as I see it's on Hardy's novel Tess of the d'Urbervilles, then sinks again when I realise we're in for more textual dissection. Another text, another exam to prepare for.
The teacher skilfully targets questions around the large class. I try my hardest to slip back into Invisible Man mode. "Stephen," she says, "tell us what happens immediately before this extract." I jump, I really do. Luckily the question is aimed at a Stephen two desks away. We get into groups. Once again, I am not exactly the star pupil. I didn't catch what the task is to be and have to ask the person sitting next to me. Concentrate you duffer, I tell myself. The look on my neighbour's face tells me it too!
So, what have I learnt in my brief bout of changing places? There's a lot of work to be done out there, that's for sure, and a lot of things to distract you from it. What the teacher does is important though. How the questions are asked -the praise distributed. And one other thing I've noticed too: how much personal scrutiny you as teacher are under from all those pairs of eyes. Sitting out there you take in everything: shape, movement, hair, clothes, glasses, jewellery, the lot. Whatever else, from now on I'll certainly be keeping a close eye on the state of my nails!