When you look at your child or are describing your child to someone... focus on the strengths. Sure, the flapping, stimming, humming etc are different than what society calls "normal" but they are all part of what makes your child unique and beautiful.
Those behaviors all have a purpose. Your child has figured out that humming or flapping calms their body down when their super senses are taking in too much information and can't sort it out. I'd say that's pretty smart.
Starting a story with, well he's in 4th grade but really 1st and ... does nothing but hurt you and child. Try thinking about it as; 2 years ago he couldn't spell his name, now he can write it! That's a huge, huge accomplishment and look how far he's come. Baby steps, baby steps.
I don't dwell in the past except to gauge our progress. What ifs... Shoulda's and Coulda's are damaging words that hurt and defeat from the moment they cross your lips.
Cherish your child for the unique miracle they are. Realize the blessing and opportunity you've been entrusted with: raise an amazing human who will touch many lives!
Other positive parenting stories here!