Sir thought he was witty

The teacher who doesn't explain things properly; the man who just writes on the blackboard; the woman who makes empty threats - children are their fiercest critics

As inspectors do the rounds of the nation's classrooms, sorting "good" teachers from "bad", they would do well to heed a few words from the experts. For the experts are all around them. Generally forgotten in the arguments that rage over teacher effectiveness, the pupils themselves are invariably their teachers' toughest critics, and they are surprisingly sophisticated in their judgements. Contrary to popular belief, the teachers they like and respect are not simply those who give them the easiest time, but the teachers from whom they can really learn something.

From a small sample of pupils aged from six to 17, asked what sort of teachers they liked and didn't like, a predominant concern was that teachers should be good at explaining and helping you to understand.

Alex, 11, who is at an independent school, finds his maths teacher "quite nasty - because when you've done something wrong, he can't understand why you can't understand it". A former primary school teacher, by contrast, he singles out for special praise because "if someone was confused, she'd try and get to them as soon as possible".

"I like teachers who teach us the way we understand, and not all gibberish," says John, 13, who is at a state school. Teachers also have to understand pupils, he adds. "I don't like teachers who don't know what you're on about."

"My favourite teacher was the one I had last year," says Jenny, six, who is at an independent school. "If you didn't understand what to do, she'd let you do your work at her desk. Sometimes I have nightmares thinking about when I get older, having stricter teachers - because if I don't really understand what to do in my maths, I'm shy to go up and ask."

Nice teachers help you, and nasty ones don't. "That's what some teachers have done to me: you ask for help, and they say go and get on with it," says Paul, 12, pupil at a state school.

Nice teachers are also firm. Young children express a little nervousness about a teacher being strict: "I don't like it when they shout, and tell you to go and sit down as quickly as you can," says Laura, six, who attends a primary school - but, as they get older, many positively welcome it.

"Teachers have got to be able to keep order," says Joanna, 12, a pupil at a middle school, "because if they can't keep order, they can't teach. I've had teachers like that - and it's chaos."

"I don't think it's a case of being strict or not strict, but it is how they are strict," elaborates Lucy, 17, who is at a comprehensive. "If they shout at you for no particular reason, then you don't like them. But if a class is being really rowdy, you don't want someone soft."

Stern judges of classroom management, pupils have nothing but contempt for a teacher who doles out detentions for petty offences - "you feel you may as well do something really bad," says Joanna - or one who makes empty threats. "Most teachers don't live up to their threats - you'd respect them more if they carried them out," says John.

Pupils are also unexpectedly acute about what might be regarded as a technical matter, known to their teachers as "differentiation".

"I don't like teachers who treat the whole class as a sort of lump," complains Lucy. "They teach everyone exactly the same way - but people are different, and have different abilities and different ways of working. They ought to personalise it more."

Even a six-year-old, Laura, fondly remembers a nursery teacher for her elementary version of "differentiation".

"I liked her because at lunch time she put you on the slow table or the fast table, for people who ate slowly or fast. I liked that, because then you wouldn't be left behind, with no children."

Teaching methods come in for some harsh scrutiny. Joanna is flatly dismissive of any teacher who relies too heavily on work sheets ("tedious little questions") or board copying ("so pathetically boring, you don't take it in"), or who sets "pointless homework, reeling off the first thing that comes into their heads, which might not have much to do with what you're really doing".

Alex is bored by a French teacher "who goes off the subject, and blabs on about something else, so you lose your concentration". John is scathing about a teacher who switched from teaching history to other subjects. "He didn't know what he was doing - he had the same book as us, and just said things from notes."

Good teachers, they all agree, know their subject inside out, and know how to make it interesting. If they are also good on jokes, so much the better. "My favourite teacher makes nice fun of people in class," says Alex. "But they don't got upset, they laugh."

Bad jokes, however, from someone who is trying too hard, incur a pitying scorn.

"Some teachers try to be funny and aren't. Teachers like that shouldn't bother," advises Lucy. "It's like they are trying to be part of the gang, but they're not, they're too old.

"You can't separate yourself too much from the class, but you can't try and join in too much, either"n