Hi ABQMom,
I'm coming a bit late to this discussion, but wanted to go back to your comment that your DS didn't realize that his answer wasn't appropriate.
My DS12 (ADHD-in and a very literal thinker) used to answer these "opinion" type questions in a similar manner -- saying he liked a certain character or story because it was "good" or didn't like another because it was "boring" or "dumb". I thought at first he was just being lazy or showing attitude, but after talking to him I realized that he just didn't understand why the teacher was asking this kind of question.
The problem was that he was answering the question truthfully, but wasn't understanding the teacher's perspective. I explained to him that she was asking this question to see if he was able to summarize part of a story that he liked or didn't like, and show that he had a good understanding of the characters and plot. He does much better on these kinds of questions now!
