Frankly, a lot of schools seem to be invested in NOT having children move too far ahead of the class, so I take their comprehension levels with a grain of salt. For example, our school seems to cap off reading levels at one grade level ahead. My DS7 reads high school/college level non-fiction and at least 4th-5th grade fiction at home, and at his school they assure me he is only comprehending on a mid-second grade level (he is in 1st), even though his DRA is by their measure at the end of second/beginning of third grade level and he frequently talks to me in detail about the books he is reading. It has become quite obvious to me over the past two years that he will not be allowed to get more than one grade level ahead. It just WILL.NOT. HAPPEN.
Part of the issue for your son may be the actual reading comprehension test the school uses. After a certain point, the DRA requires written answers, not oral, and it can be difficult for some younger students, no matter how bright.
Some of the other behaviors sound typical for 5.5, but pursue an evaluation if you think it is necessary.
