Thought I'd give an update after 3 years
DS is now 8. Gone through psychoeducational assessments recently. Scored ~99.9th percentile on FSIQ and GAI (WISC-V) and ~99.9th percentile on WIAT-IV. Processing speed is still the lowest, but has improved a lot to ~75th. Now I have proof he is indeed twice exceptional.
COVID/remote learning changed a lot of things. Ironically distance learning seems to have helped DS by pulling him out of the chaotic classroom which had many triggers for him and thus allowing him time to catch up/mature. About a month into distance learning, he saw something at home that reminded him of the classroom and had a breakdown. That's when I realized how traumatic the school experience was for him. His disruptive behaviors were emotional responses and a form of defense. 2e kids deserve the benefit of doubt and more kindness.
DS is a lot calmer now and we are in a better environment where teachers and staff are more understanding and accommodating. He was happy to go back to school in person, seems to enjoy school activities and social interactions, just not the "work" part. He has 1-on-1 para for half a day who helps him with emotional regulation e.g. daily check-in, take him for a walk to "get his wiggles out", or scribe for him when he's unwilling to use a pencil. Not perfect, but he's coping. He seems to get singled out a bit among peers, partly because of his behaviors (e.g. he'd blurt things out loudly in classroom, move his body/hum a tune when reading/working, make loud noises kicking his desk), but I'm not aware of bullying so I'll let him get feedback from peers regarding his behaviors. I believe homeschooling would be better for him academically, unfortunately I'm not able to take that on, and can't recreate the same social-emotional learning experience by myself.
DS still struggles with writing. He can't put his thoughts on paper, or write legibly. Work completion is a big concern, but I suspect he's partly using it to get adult attention. He does better when he's given ample time, allowed to type, and write on a topic of interest.
DS loves books, can read above grade level, especially non-fiction, science books. He doesn't seem to enjoy fiction as much, other than silly/funny stories. So as a third grader, he's reading fiction at 1st grade level, non fiction at middle school level essentially. I have yet to find a good sci-fi book at his reading level that he would enjoy.
Another COVID era "gift" is that he got more comfortable with computers. He uses google and youtube as his research tool on topics of interest. I check his search/video history, and I'm generally ok with his screen time. The only concern I have is that he hasn't developed the ability to filter out misleading information, so parent monitoring is still essential.
We finally visited a developmental optometrist (2 years late thanks to COVID). Just as aeh had suggested, DS has visual tracking and convergence challenges. He's still going through therapies and progress seems to be slow.
I haven't talked to DS directly about his twice exceptionality, although he's gradually figuring things out himself. He realized that if he "behaves", he'd lose his current 1 on 1 para time. Ugh. He doesn't seem to be motivated to work hard, and I don't know what to do about it.
My biggest challenge now is to find the right level, the right amount, and the right kind of challenges for him. He needs to learn to endure boredom, sense of defeat, and a range of emotions while going through repetitive practices to be able to achieve anything.
It is hard to be a parent of a 2e kid. I am truly grateful for this community. I wouldn't know where to find the same kind of understanding, support, and guidance anywhere else.