Technology is well and truly on the side of this generation of children.
I have just discovered Digital Voice Recorders, primarily for using in my own journalism work, but I have found that they can be a great tool for helping written output disorder too.
Children can in the first place record their stories, say maybe three times, each time the story will improve. Then they can either transcribe what they have written with less frustration because they can get the words out.
Alternately they can type the story out.
There are even some recorders that will synch with Speech recognition software like Dragon Naturally Speaking. (Research this carefully before purchasing a model)
From my reading the most recommended models are Olympus Digital Voice recorders. I have just purchased a cheaper one in the Olympus range VN2100PC. Be sure to buy one with PC in the name, as that means it will download to a PC via a USB lead.
There are a few considerations: parents may be nervous of it getting lost/damaged in the classroom. Some may come with a neck strap. They would fit snugly inside a cell phone holder for added protection. The teacher could agree to store it in their desk.
I should add that a digital voice recorder is not the same as an mp3 player because it has an external mike jack and therefore the sound quality should be better. However I believe there are many mp3 players on the markets which include a voice feature, so there is a viable alternative use also.
The other choice is to keep the Digital Voice Recorder specifically for use in the home with homework assignments. Another purpose to this technique is to counteract the frustration that children with written output problems can experience.