Storybird is an excellent site to help students to write. Although it looks more for elementary students then anyone else, it can be used for any classroom for creative writing. The site has tons of pictures that do make sense in a way if the student uses his/her imagination, and comes up with a theme. The site helps students understand the procedure for planning (getting what pictures in what order) and also gives the thrill at the end of publishing their work for others to read and critique. The feedback is amazing and fun as much as the creation of the story. For an example look at http://storybird.com/books/the-flying-chair/ a quick one I made for students to use as an example. I tagged it as "example" and made it public. This program can also be used for other languages. And the teacher can set up a class for his/her students where there are assignments in the class set for students to complete and email the address for the teacher to mark their work. Click here for notes on how to set up a class StoryBird for team story writing.....
Some good points of the site, its quick and easy to do. Students can do public or private stories. There is the ability to collaborate, for sharing in classroom setting (see above). The pictures can be organized by the students (you can move things around). You are able to add pages inside your story - not just continue to add after the last page. As long as students are on the page where they want the next blank page to enter, you just hit "add a page" But give the students time to register because it's by email and it takes a while for the email to come to you. Save the stuff often. The system does save on it's own and when it does this all the pictures go back to a different order from what you organized.
It took me 1/2 hour to do the story example listed above. I still don't know how to mark students with this assignment as I'm not an English teacher but if someone has an idea, please submit it to me by email and I would be happy to add it to this page.
Attached is some instructions for you to hand out to your students. And below is a video made by Storybird to help you understand what it can do.