It sounds like he would benefit from a highly structured writing approach that uses rules or guidelines to help expand his writing. My son's school uses a rules based approach that appears very "canned", but once the student is in the habit of following the recipe, they are able to customize and personalize their writing.
For instance, when writing a descriptive paragraph, he must include a topic sentence that is the subject or key idea and at least 3 attributes each which are supported by 2 details. For example: To survive, humans need shelter, food and clothing. (main idea) Shelter helps to protect them from the weather. (attribute). It can keep out the rain so that tools and food do not get wet (SD #1) and it can protect them from harsh cold and heat.(SD#2)
There are many graphic organizers that help with this. Inspirations is available to students and parents and offers an on-line tool that he could use with a computer.
As aculady suggests, he should also be encouraged to use descriptive and strong vocabulary. My son has a list of R.I.P> (rest in peace) words that he CANNOT use. Words such as good, nice, stuff, went.
An editing checklist is also helpful. The checklist would contain the KEY (not every) errors that he should check. It should be based on whatever skills he is working on. For instance, my son is working on maintaining the same verb tense throughout a paper, and this is one of the items on the check list. He also has the RIP words, and use of commas for lists and compound sentences. He makes plenty of mistakes, but his check list is limited so that he can concentrate on just a few things at a time, master them and move on to other issues.
Hope this helps!
