Exactly that really. DD is 6 and on level 16. she is struggling with comprehension as she has no frame of reference for half of what they are talking about. School will not allow her not to read levelled books . does anyone know if there is a series of books written especially for young advanced readers? TIA
I'd second the classics - there are a lot of books out there suitable for an advanced 6yo reader. My DDs were very like yours, OP - they read the Hiccup Horrendous Haddock series, the Septimus Heap series and some of the simpler Diana Wynne Jones.
School put DD2 back on ORT this year (she's in Yr 5 now, school was having to prove the point to OFSTED) and she was not impressed, but she ploughed on through and kept on reading for pleasure and the school have now given her Inkheart by Cornelia Funke, with the promise of more similar reading to follow. (not something I'd recommend for a 6yo though, DD2 is almost 10)
I second kistigger's view of letting children choose their own reading material - it's so true that even a very advanced reader can sometimes spend weeks or months reading stuff which is way too "young" for them, or which is just plain drivel. Our local independent bookshop has been amazingly helpful at suggesting books - my DS2 prefers reading series, so it has often ended up with buying the first couple and getting the rest from the library. Parents of slightly older children were also a very useful resource and we've borrowed a couple of entire series that way.
The Beast Quest books were very helpful to us when there was a mismatch between DS2's comprehension and reading ability (the stories are IMO utter drivel once you've read the first set of six, but he loved them and only gave up at about book 42). Horrid Henry was also a great favourite at the age you mention, also the Roald Dahl books. I have a feeling that DS also read the first couple of Harry Potter books at age 6, although I think they were really too hard for him and it was more a case of dogged determination.
As for the question of "adult" content (which the op didn't really ask about) I think there are just two types of parents, one who feel it's important to know that their kids are able to deal with stuff before they read about it in a fictional setting, and the other type who thinks that the written word probably can't do much harm, especially when you think about all the other forms of crap that children are exposed to, and the benefits of developing a reading habit.