Urgh! I just came on here to ask the same question and I am not inspired by the answers I read here. I have just been shopping for clothes with my 13 year old dd. She stated on the way there she did not really like M&S anymore - fair enough, what teen does? But we went there anyway as she needed new bras. She is only a 30AA, so not at all busty.
She then tried on some clothes in M&S and was very pleased with a flippy skirt and a t-shirt to match. All's well so far. But she needed loads more clothes - she has basically outgrown everything.
We tried: New Look, H&M, Gap (altho she said she did not like it anymore, it is the only place that sells jeans that are skinny enough to fit her - we got a pair of jeggings for her there), Animal, Top Shop, River Island. Nothing even remotely suitable for a 13 year old in any of these places.
She hates Next (as do I) and we were in Primark a few weeks ago and again saw nothing but slutty t-shirts in horrid fabrics and colours.
She wants a new swimming costume, possibly a bikini too, some dresses, some jeans (I should have bought her a pair in Gap but they were so expensive so I was hoping for something cheaper) t-shirts, skirts, shorts - the lot really. I really don't get where 13 year olds buy clothes from. Dresses she tried on in New Look were way too long on her (I reckon she is probably about 5 feet tall). She has small boobs but big enough that she cannot wear children's tops/dresses, no hips, and has pin-like legs (so most leggings are baggy). She doesn't want to wear children's designs or pink or black or anything tarty or slutty.
I am at a loss as to where to look, and so is she. Sorry for rant. Was going to start my own thread, but this one seemed to be about the same thing. 
