rosbo, my dd (15 now 16) was all set to go to sixth form here in our town last september.
we discovered by chance a boarding school (we are not in UK) with a technical course in her most favourite subject. She was completely hooked on the idea from the moment she looked at their website.
So, although we worried she might be too young, we let her go. She is not remotely academic and a little irresponsible (though not into alc or grass as far as we know!!!), the deal was that she could go as long as she actually studied. If not she would be home again in a flash.
She adores the place and is focussed on the future and maybe university. She would have been bored stiff at the local 6th form college. and you know when teens are bored....anything can happen.
We make a big fuss of her when she comes home, send her goodie parcels, call her often, tell her we're proud of the way she's managed.
We have two younger kids in the house so I do wonder if she's not had enough attention over the years. Still, I really know she's happy there, and happy when she comes home.
the key is - she really really wanted to go!
if you can find something/somewhere your daughter desperately wants then you might be on to a winner.