You've been given lots of great advice already, so this is just more commiseration...
Your son's situation almost exactly mirrors mine's. DS7, who is also very science-y, also began crying (brokenheartedly) about never learning anything at school.
Last summer I went to the school armed with writing samples, a write-up of his personality & accomplishments (playing 3 instruments, youngest member of youth orchestra, took 2nd grade EPGY math over the summer, etc). They already had his IQ scores since they're the ones who did the testing. They had his reading scores showing he was above grade level in reading. I stressed that he absolutely did not need any phonics instruction and since he'd completed 2nd grade math, could he skip to 2nd in the fall? They agreed, and DS and I were so excited.
Well, a couple months into the year, he began complaining of boredom and finally broke down in tears. My conversations with the teachers went nowhere. I could have gone back to the Asst Principal (who okayed the skip) to push for more challenge, esp. in math, but I decided to withdraw him around Thanksgiving.
(He made it through K the previous year with a lot of grace and patience re: learning material, but I think he just couldn't take it anymore - not being challenged, that is.)
I no longer work from home, so I couldn't keep him with me, but my mother agreed to care for him during the day while he did the work I sent for him.
So he is now happily homeschooling, and gets to do science EVERY day.
I am all for after-schooling--that's how we made it through K. But, at some point, like you or someone else mentioned in this thread, it's hard on kids for most or all of their learning to happen once school lets out for the day (esp. if there are other after-school activities on your family's plate).
If your DS can homeschool, maybe even just for the remainder of the current year until you find a better school/sort out the appropriate classroom environment at his current school, etc., that might be best.
My son was wilting - there's really no other way to describe what I witnessed - but like your son, he's very good about expressing himself. So it's great he has YOU to listen to him and make sure he gets what he needs.
:-)
