While I disagree with taking him out of school, I think the rest of your ideas are solid. Here are a few more thoughts...
1. Is your son getting enough sleep, as in 8-10 hours?
2. Is your son eating healthy, fresh foods. You might consider taking sugar, sodas, junk food out of his diet for a while and see what happens. Maybe consider some allergy tests?
3. Review his routine. Does he have a rock solid routine that he can count on?
This next suggestion is one I stumbled on when my "marches to his own drum" son hit a particularly bad year at school (2nd grade). We called it "popcorn" time. At the end of each day, my son and I would cuddle up and play "popcorn." He would say "popcorn" and I would gently tickle him, get him laughing. I'd stop when he said "stop popcorn." When we were content with our laughter, I would hold him close and tell him all the wonderful things he did that day, all the wonderful character traits I saw in him. It was silly and horribly misnamed, but ending the day with cuddles, giggles and compliments really took the sting out of spending the day out of sync with the rest of his world.
Additionally, you may want to consider that "marching to a different drummer" is a life-long thing, not something that is fixed within a year. Think marathon, not a sprint. For me, I had to learn to work to my son's strengths and help him find coping skills for his weaknesses. For example, my son performs best at school when he's NOT in a group. He doesn't suffer fools well and often exploded in class when kids were just being goofy, immature kids. In fact, he's the kid who could work quietly by himself in the hall and still get a fine education. We had to teach him to recognize his "danger signals" (as in, "I'm feeling myself get angry" or "I'm about to explode") and then ask the teacher for a time out to cool off. If it was recess, we taught him to just walk away and take some time to himself to regroup (the deep breathing techniques we taught him also worked). It took a lot of years and a lot of hard work, but now, in the 8th grade, he does a great job advocating for himself. If I'm dealing with teachers, it's about grades, not behavior.
Another strategy I used are "goody tickets." My MIL used these with her brood of 5 kids, three of whom were special needs kids. When a child is "caught" doing something well or correctly, he earns "goody tickets" which are then "cashed in" for a treat, such as play dates, tv time, or whatever your son enjoys doing. If punishment (the "stick") doesn't work, this technique offers an incentive & reward (the "carrot"). I had his teachers involved in goody tickets from preschool forward to about jr. high school. All but two of his teachers loved it and it was those two where he struggled the most. Goody tickets combined with significant training on doing something because it's "the right thing to do" is best. My son now does many things he hates because he's learned "it's the right thing to do." Again, it takes time.
Whatever stratgey/strategies who choose will take consistency. But, I know you know that! <wink>
Sorry, this is much longer than I expected. Good luck.