Differentiator is a site that is really gaining in popularity over the eduverse/online world. While it is a simple site to use, it really is neat in how it uses Bloom's Taxonomy to generate "meaningful" sentences.
I think there is some potential here which can help users learn how to structure a "proper" sentence. For example, each sentence starts out w/ the words "Students will ....", the user then clicks on a word in each of the following categories: Thinking Skill, Content, Resources, Product, and Groups.
Below is my final sentence...
Students will define the change over time of using websites to create a timeline in groups of two.
Give Differentiator a try by clicking here.
For another detailed review check out Larry Ferlazzo's blog.