Another idea for the fast thinkers. There is dictation software on the market today. The kind that types as you talk. If your child is reluctant to write because they think too fast, this might help. If the child can see on paper what their story is like. It might give him/her the confidence to write on their own.

As your child reads the story they may even come up with better or more detailed ideas.

Just a theory.

http://www.giftedandtalentedsociety.com/content.php