Teacher and children jokes! 
The humour here is linked to the humour of waiter, waiter jokes. First, like the waiter, the children do not give the sort of reply that
the teacher or parent (and the people listening to the joke) expect. Second,
we expect teachers, like customers, to be in control of what is said in
the classroom. But through (deliberately?) giving alternative answers,
the children are disrupting the status quo.
1. Teacher: Children, what do we call someone who talks about things that
no one else is interested in?
Children:That's easy. It's a teacher!
(Because teachers are boring...)
2.Teacher: Children, if I had ten apples in one hand and seven in the other,
what would I have?
Children: That's easy. Big hands!
(You didn't think the answer was 17, did you? The teacher did!)
2.Teacher: Children, if Johnny had ten pounds in one pocket of his trousers and seven in the other, what would he have?
Children: That's easy. Someone else's trousers!
(I thought the answer must be 17 this time.)
No, Johnny would never have that much money in his pockets!
3. Teacher: Children, how do you spell chrysanthemum ?
Children: But teacher, we can't spell either!
(Surely the teacher can spell chrysanthemum)
But she's always asking us to spell words for her! If she can spell a difficult word like
chrysanthemum, why is she always asking us to spell things?
(Also: A: Constantinople is a very long word. How do you spell it?
B: C-o-n...A: NO: I-t.[B goes red with embarrassment; A rolls about laughing.])
4. Teacher: Children, when I ask the next question, I want everyone to answer at once. Here is
the question: How much is eight times seven?
Children: At once!
(Will the teacher ever get the answer she wants?)
Surely she doesn't expect us to do her tables for her as well as her spelling!
5. Teacher: John doesn't seem to be here. Does anyone know if he is missing school today?
Children: He's in bed with a cold, but he's not missing school, miss!
Teacher: How can he stay in bed and not miss school?
("To miss something" has more than one meaning. If you miss a train, or miss a television program that was broadcasted yesterday, this means that you
wanted to catch the train, or watch the television program, but were unable
to. You were probably late for the train, and may have forgotten the television
program. If you are absent from school even though you are meant to be
attending, you "miss" school.
However, if you miss your high-school friends, or miss a television program that has been canceled, this means that you are sad
because you do not see those friends any more, or because your favorite
television program is no longer being shown. If you do not enjoy school,
you will probably not be sad if you are absent. In other words, although
you are missing school, you are not really missing it. The teacher and the children are talking at cross purposes, as usual.)
6. Teacher: Children, I have never seen such dirty hands! What would you say if I came into the classroom with hands like that?
Will the children say what the teacher expects them to say this time?
Children: We'd be too polite to mention it, miss!
(Presumably, the teacher expected the children to say "Your hands
are very dirty! Please wash them." But, as the children point out,
it is not very polite to say that to someone, particularly to a teacher...)
7. Teacher: Children, why are so many of you late today?
Children: It's not our fault, miss! We were only doing what the lady with the sign said, miss. You told us that we must always obey grown-ups wearing uniforms,
miss.
(The "lady with the sign" is a "school crossing guard",
in American English. Her job is to stop traffic so that children can cross
safely on the way to and from school. Her sign was meant to stop traffic,
not children...)
8. Teacher: John, I am sure I have read this essay about your dog before. Isn't it
exactly the same as the one your sister wrote?
John: But that's because it's exactly the same dog, miss.
(I wonder why the teacher is tearing her hair?)
9. Father: How was school today, children?
Children: The teacher gave us both a bad mark for something we didn't do.
Father: That sounds rather unfair. What was this "something"?
Children: Our homework...
[Their father was getting ready to complain to the teacher, but what's going
to happen now?]
10. Father: How was school today, children?
Children: The teachers know even less than we do, so we've decided not
to go back again.
Father: Why do you think that the teachers know less than you do?
Children: All they do is ask us questions!