Pure magnetism

It's last lesson Friday so it must be Maths with a bottom set of 13-14 year olds. One of them was particularly late and there are a wide variety of lame excuses, but this one was a first.
'Why are you late?'
'I was in Science'
'And?'
'And we were doing about magnetism'
'And?'
'I brought a magnet away with me'
Now this was a fairly substantial magnet he produced from his pocket, it was maybe 5cm x 3cm x 2cm. This still didn't fully explained why he was late and still looked flustered.
So another 'And?' was needed.
'And?'
'And my friend has just had braces fitted to her teeth'
'Please tell me you didn't...'
'I'm sorry sir'
So in a quest of scientific discovery this pupil had stuck a huge magnet to a girl's braces. He had then spent the time inbetween lessons trying to prise it off. The girl had apparantly been a bit uncomfortable during this process as it was a strong magnet and she could feel her teeth being pulled along with the attempts to remove the magnet. Ouch!