My year 8 dd really needs her sleep, so for her 10 hours is perfect. However, she has a long school day (independent school) and a couple of time intensive activities outside of school that she does not want to give up. This means she is pretty busy and during the week gets about 9 hours sleep, which is just enough but not ideal. She looks tired and sometimes I worry about it. But I think some of her friends get even less...