Fantasy writers including Philip Pullman, Terry Pratchett, Alan Garner, Darren Shan and Neil Gaiman have expressed their opposition to proposals to add age bands to the covers of books published for children in the UK. One of their many issues with the proposals is that children may reject certain books for fear of being thought babyish, while others will find books of their "correct" age-group too challenging, and be put off reading even more firmly than before.
Pratchett had this to say: "When I was a child I read books far too old for me and sometimes far too young for me. Every reading child is different. Introduce them to the love of reading, show them the way to the library and let them get on with it. The space between the young reader’s eyeballs and the printed page is a holy place and officialdom should trample all over it at their peril."
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Personally, I'm against this age-banding idea. I think it could lead to kids unwittingly categorising books in a negative way - "Oh, no way I'm reading that book - I'm 10 and it says 6-9 on it." This could easily lead to kids missing out on books they would have otherwise enjoyed.