I took a look at this website and then checked around for prices of the recommended Toshiba. Could not unfortunately find anywhere that had it in stock but found the latest model at Tesco Click Here. The top listed model on that page is a 17" screen and may be a bit heavy for a 12 year old to carry around. The maximun size I would go for is 15.6" and I would suggest that you get one with a DVD Player/Writer built in. Get a well padded carry bag either back pack or with a good strap, it will get knocked around at school.
Sony Xperia Z5 review: Hands-on with the phone which the Z3+ should have been