This is a really good question and one that is not easy to answer. I spent most of my teaching career as a secondary level English teacher. Writing, especially formal style, is tough these days due to the graffiti language that students learn via video games and text messaging. I'm not sure which grade you are targeting with this question.
Secondary level - there is an interesting lesson entitled Beyond "What I Did on Vacation" which might make a good writing prompt for the beginning of the school year. Students always write better about things they know or have experienced.
Rubrics were a way I could differentiate instruction. I would create the rubrics according to various instructional needs. You can search for rubrics within Thinkfinity or Rubric Maker is a great resource for creating rubrics online and then printing them. Using Graphic Organizers is another way of helping students with writing and different organizational methods work for different students.
Thinkfinity also offers some interactives which may assist with lesson planning for various instructional needs.
Literary Graffiti This student interactive, used in several ReadWriteThink lessons, encourages students to create literary graffiti corresponding to a piece of literature they have studied.
Fractured Fairy Tales This interactive tool gives students a choice of three fairy tales to read. They are then guided to choose a variety of changes, which they use to compose a fractured fairy tale to print off and illustrate.
ReadWriteThink Notetaker This student interactive, used in several ReadWriteThink lessons, provides an outline tool that allows students to take notes while reading.
Comic Creator The Comic Creator invites children and teens to design their own comic strips. Their creations can be just for fun or as part of more structural learning activities: planning writing activities, before- and after-reading activities, and responding to books.
If you search thinkfinity.org for writing lessons and writing interactives, you will find resources that may help you with your question. The ReadWriteThink partner site has 55 student interactives, and many of those are geared toward writing assignments. Sometimes with students who need different instructional methods, it's just finding the resource that helps them think and learn in their own way.
Hope these suggestions will get you started for the year.
Verizon Thinkfinity Community Host
We just recently published a new series of strategy guides on ReadWriteThink.org focusing on differentiating instruction: http://www.readwritethink.org/search/?strategy-guide-series=30099.
Hope these provide some helpful information for you. If you are interested in submitting a new strategy guide for this series, please contact us about contributing at http://www.readwritethink.org/util/contribute-to-rwt.html. We offer a stipend for materials published on the site, and would be interested in adding your expertise to this topic.
Many thanks for opening this discussion. I'll be adding myself to the thread to hear what others have to say.
I have my students create short stories based upon their specific interests. One student wrote a story about her dogs who are sisters. Another student wrote about teddy bears really being angels who looked out for her. Students have also written different endings to stories read or heard in class and others have discussed and then written what they would do if they were a character in one of the books they read in class.
Hope this helps!