This school has produced Levels and Skills Descriptors for Years 7 and 8
www.didcotgirls.oxon.sch.uk/103/english
Science doesn't seem to have been done yet. Basically they are saying that if your child can do things in a particular band then that is the grade they think they are looking at for GCSE - obviously there are a whole load of caveats here.
Thought this might be useful as so often people aren't sure how well their child is doing and this may give them some idea.