My teenagers never bothered to blame it on the school 
When dd was about to start year 7 I went to great lengths to find a coat that fitted into the uniform list.
It had to be no shorter than waist length, no longer than mid thigh length, navy blue, no logos or writing of any sort, not quilted or padded and have a hood.
So I finally found something that fitted the description. She wore it on the first day. Came home, coat was stuffed in the bag.
The next day she left it at home.
I said "why aren't you wearing your coat, put it on you will get cold"
She said ok, I imagine she stuffed it in her bag again because the next day I said put your bloody coat on and she said, look mum, ill put it on to leave the house. But I'm just going to take it off at the bus stop. It's not cold, I don't like coats and it takes up too much space in my bag.
I sold it on eBay a month later.
When DS1 started year 7, I didn't bother. He had a coat, it was the wrong colour, the wrong material and had a logo on it.
He wore it twice.
Now dd wears about 7 layers under her uniform, DS wears football skins and a hoodie and I don't bat an eyelid.
Yes, they are cold. But I am not because I wear my coat!