Flash fiction is the term we use for short stories that are really, really short. Stories of a thousand words are usually in the upper limits of flash fiction, but it is often much, much shorter. There are anthologies of stories of fifty words or less, for example.
Other terms for flash fiction include: postcard fiction; micro fiction; sudden fiction and short short fiction.
2012 saw the inauguration of the first National Flash Fiction day. This year it will be held on June 22nd. You can access the Flash Fiction website by clicking on the link here.
As well as various U.K. based events, there is a Flash Fiction competition, entries for which have now closed for this year, but you might be interested in celebrating in school by running your own Flash Fiction competition. In the Arts Council sponsored competition the upper word limit was 100 words.
Writing stories as short as this can really help children learn to focus on what is important about a story. There are key elements a story has to have to work, so that readers understand it. When there is no word limit for a story it is possible to get side tracked and leave out vital information. When you have a word limit of fifty or a hundred words you have to work out very early on what you need to keep and what is extraneous information.
There are various examples of Flash Fiction you can access, both in anthologies and on the web if you are looking for ideas. You can set a theme that ties in with a topic you are currently teaching, or you can give your children free rein and see where their imagination takes them.