My daughter can't lie, or embelish the truth, at all. If I'm not convinced that she's telling the complete truth, I only need to say, 'Is that true?' and she says, 'No, it didn't really happen'. She doesn't do it very often, because she knows there's no point in trying.
I have a worry about a child in her class, who is a habitual and convincing liar. He has said false things to the teacher about my daughter (and others) doing X or Y and the teacher believed him. He tells fibs about having an older brother and living in a flat, etc. We live very near to him, so my daughter knows a lot of what he says is just not true. A lot of this sounds like he's a Walter Mitty character, but some of his lies have been dangerous and he's also been involved in a very serious incident, so serious that several parents, including myself, have told their children to keep back from him. So, he's definitely one to watch out for. However, until this morning I thought he had a very pronounced stutter. But, my daughter told me she can tell when he's lying. She imitated his stutter and said that he talks like that when he's lying and he did not usually speak like that. This knowledge will be of great benefit, I'm sure. They've jut got some new teachers, so we'll see if they're taken in by him.
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"We act as though comfort and luxury were the chief requirements of life, when all we need to make us really happy is something to be enthusiatic about." Charles Kingsley