Concerning the writing issue:
Is it that he has a problem writing the *kinds* of answers he wants to write? For example, most of the other kids might want to simply respond with "It is scary" while he wants to write a 6 year old's equivalent of a dissertation on the difference between white and nurse sharks. It's tough for a 6 year old to write that much, even if there aren't LD issues involved. He might also know the right words and their meaning, but not how to spell them (and if perfectionism is present, then we all know that a 6 year year old will believe he should spell everything correctly the first time).
I've just noticed with my child that sometimes the quality of the answers he wants to present can actually inhibit his ability to respond.