God! That is shocking and I can't even begin to imagine how awful having to go through that at the age of 8, and to be treated like that by a adult who's supposed to be looking after you. That teacher should've be sacked and struck off.
When I was in the latter years of primary school, my best friend started her periods at the age of 11, and believe me, I was jealous. There was a couple of other girls too. Our family weren't well off and for pe lessons you could wear shorts and a tshirt, but if you didn't have those, then it would be vest and pants. I was one of the vest and pants brigade. I begged my mum to buy me a pair of pe shorts and when she did I was so thrilled. First lesson I got to change into them, my friend approached me and asked me can I lend my shorts to Julie because she's in the toilet and she's just "come on" - I didn't really understand what she meant but I said no, I want to wear them, so I said can't you lend her yours, she said she was "on" as well. In no uncertain terms she told me that if I didn't lend her them she'd never speak to me again, so off they came! Horrible experience!
When it happened to me, I was nearly 15 and I was in the cinema with some friends, I felt a bit yucky down below, went and checked and lo and behold. Didn't have anything on me just in case but was ok till I got home, no great drama. Right age for it really I was lucky!