Write Stuff
We are very lucky in Guernsey to have an amazing annual writing competition in The Write Stuff which gives excellent opportunities to students of all ages to hone their writing craft.
Their website is excellent and has a comprehensive archive of some of the best stories - look in particular at the intermediate and senior categories (one or two EC / LC winners!):
Competitions - Poems on the Move, Write Stuff - Guernsey Literary Festival
BBC 500 words:
For KS3 pupils, the BBC's 500 words competition offers some superb prizes and has excellent resources and a full archive of previous winners: