You've received excellent advice already, but the one thing I'd add is - middle school was hugely different for my kids than elementary in terms of being able to cope with being gifted and not being skipped (we didn't skip). Does middle school start in 6th or 7th grade where you're at? Once you are in middle school, having multiple classes allows for options to subject accelerate, as well as having language classes etc (depending on where you're at) - for something different. Our middle schools also grouped by ability, which didn't give EG kids a class full of other EG kids, but it did mean that all of the kids who were just barely treading water were no longer in the same class, and that can make a big difference.
If you can consider private school or charter schools, check out what's available in your area. It's possible that you might find a different school with a different set of teachers or different teaching philosophy works better for keeping your ds engaged in a way that would still allow you to avoid a grade skip.
I'd also consider whether or not a grade skip lands him in a mixed-ability classroom similar to where he's at now. The challenge for my kids, when they were subject-accelerated around the same age, was that the wide range of abilities in the classes they moved up presented issues that were similar to what they were frustrated with in their age-appropriate grade level class - the class had to work at the pace of the kids who didn't get it rather than let the kids who caught on easily fly.
So - a few things to consider if you're on the fence re the grade skip.
FWIW, I have one competitive athlete among my kids. She's lucky to be pursuing a sport that has competitive leagues up through high school (and where her chances of being challenged in the sport are better outside of playing high school sports)... but fwiw, I wouldn't want to let her skip ahead a year knowing that it's likely she can participate in her sport in college and might be eligible for a scholarship in it (totally knocking on wood here lol!)... that one extra year of prep and maturity will help her be ready for college competition in several ways, physically and psychologically.
Best wishes,
polarbear
ps - I wonder also - is it possible that part of the reason your ds is struggling much more this year with wanting something more in school is partly related to this year's teacher or class style or something other than only high ability? If he's been satisfied in previous years, it's possible he was just putting up with the status quo, but it might be that he also had teachers who understood how to connect with him and challenge him, and maybe this year's teacher just doesn't get it.
