A very nice way to demonstrate the long-term effects of bullying.
A sheet of paper per child
A teacher in New York was teaching her class about bullying and gave them the following exercise to perform...
She had the children take a piece of paper and told them to crumple it up, stamp on it and really mess it up but do not rip it.
Then she had them unfold the paper, smooth it out and look at how scarred and dirty it was.
She then told them to tell it they're sorry.
Now even though they said they were sorry and tried to fix the paper, she pointed out all the scars they left behind. And that those scars will never go away no matter how hard they tried to fix it.
That's what happens when a child bullies another child - they may say they're sorry but the scars are there forever. The looks on the faces of the children in the classroom told her the message hit home.
I expanded on this a bit after some observations of little things being said to a person going "viral" which annoyed the person and his mum, but without the kids realising they're almost teasing the kid.
We all sat down in a circle, and I asked everyone to draw a simple picture of their face like a stick-man/cartoon.
Referring back to the camp, I said how something perfectly innocent can upset someone. To mime that, we passed the bits of paper to the next person, and folded the paper once.
"Now, because the thing was funny, someone else overheard it and repeats it to the person", and we pass the paper to the next person and fold it again. Repeat a couple of times.
Ask the kids to open up the paper and look at the face - it's damaged.
Tell them that the line between having a laugh and teasing can be very fine and that line is different for everyone. Pass the paper round and the kids now lightly scrumple it up, teasing.
Teasing quickly becomes bullying, so pass the paper round, really scrumple it up, stamp on it, do anything but rip it.
Now, because we are scouts, we say an important word (prompt for kids, who will say sorry), and we do our best to help the person by smoothing out the creases.
Then finish off as above, pointing out that lasting damage has been made etc.
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