Hey, the fact that you recognize the issue and have asked for feedback is awesome. Go Dad! Lighten up on yourself too. 
Three hours a night is way too much. It’s better to let your kid mature into handling the pressure than prematurely cracking him under the weight of it.
“People keep saying that “it is only middle school”. In our magnet middle school kids take high school courses starting in 6th grade. Lots of parents have their kids repeat a course if they even get a B in Middle School because they know it will go on their HS transcript.”
And yet amazingly they wind up at the same colleges studying with the kids who went to plain-jane public high schools. Imagine that.
Why is it all such a race?
Yes, OP deserves a lot of credit for being open to personal assessment.
Please, block the grades site from your computer. For your sanity and his.
He needs a dad, not a college coach. It’s really that simple. Hang out with him. Do fun things with him.
3 hours of homework is way, way too much for a 12 year old.
@tv4caster I don’t think the issue is that it is “only” 6th grade. I have had kids taking high school classes in 5th and 6th grade. I think the issue is in the amt of homework for a 6th grader. My kids performing at that level still have the lives of children. Performing at thst level wasnt due to Herculean effort or time. It was who they are.
There is a disconnect between age appropriateness and workload.
(On my phone which is not letting me edit. Forgive mistakes)
Grades don’t matter. Outside of HS and a few paths in college, they don’t matter. Especially now in middle school. Determining what he’s interested in, willing to work for, enjoys. They will change, but that’s important.
@Mom2aphysicsgeek I agree. I was just pointing that out since a few people didn’t seem to understand that some of those course count.
3 hours seems excessive. My kid had lots of work in MS compared to her brother and sister, but it wasn’t 3 hours worth.
Edit to add @thumper1 response
I wasn’t saying I thought it was ok. I also never said to prevent him from being a 12 year old. I specifically said there needs to be a balance.
Ask him if you can meet with him and his teachers. Maybe they have some ideas of how to help him.
Stop checking his grades so frequently; that’s your problem, not his.
And try to figure out why he is getting Cs - is it test scores, homework, something else? Is 3 hours of homework per night because he doesn’t understand, or is there really that much work? Or is it busy work?
If you ask his thoughts on it, maybe he would share with you. Is he bummed about quitting basketball? Or does he really have trouble with the material?
The more he is involved with the decisions in his life, even if you are influencing him towards a certain path, the more he will do his best.
(To be honest, I’d get a copy of his homework and try it myself, and figure out if I thought the amount of homework was too much or my child was missing something. Not saying to hand it in for him, but do it yourself to see if it is really high-level.)
@pizzagirl you took the words right out of my mouth!
I read stuff like this and I am incredulous. My S was admitted to Princeton SCEA and will undoubtedly have many additional options when RD decisions come out. It would be a stretch to say that he has EVER done 3 hours of homework in an evening, never less in every night in 6th grade. In 6th grade he was playing with Pokémon cards and watching Nick Jr. after school.
It will be important for the OP to think through the difference between, and relative importance of “excited by learning” and “gets straight As.” Don’t you want your kid intrinsically excited by learning? And at 12 yo that could be dinosaurs, outer space, so many things. Isn’t THAT what you want to nourish?
Short answer is that this is madness, and in no way good in short or long term for parent or child. You asked our opinions; as a parent and educator this looks to me like parental malpractice.
I am going to disagree a bit.
My 2 oldest went to one of the better public HS in our district, and over the last 5 years I do not know of a single kid who got into an Ivy. I only know of one who got into Stanford.
So, let me give you an example of why some people think of it as a race (and I admit I have to work not to fall into that category sometimes). Kids from our public high schools get into some top colleges, but there aren’t many of them. Every year there are a very few from the entire district who get into Stanford, or MIT, or an Ivy etc. and they are almost always the product of one of our magnet schools, and not one of our "plain-jane’ high schools.
There are usually 1 or 2 per school who get into the next slightly lower tier, like UNC or Duke (or something similar). A larger, but still small number, get into our top ranked state school (UVA). For my oldest 2 kids grades it was only about 10-13 who got in there. At my youngest kid’s school it is probably 2 or 3.
I know that the vast majority of the cases that I listed above, that the kids who got into those top schools were the ones that were in the magnet schools in elementary or middle school (at least that has been the case with the many dozens of kids we have known over the years who went to top 20 colleges). Because of that, there is a race to get your kid into those magnet schools.
Because our district screens for the smartest kids, and then segregates them in elem and MS, you end up with a higher percentage that go on to top schools versus the non-magnet students. Because our district also has a few “magnet type” high schools (IB, STEM, etc), the smart kids are also somewhat segregated in HS.
I would venture to say that very few of the kids in our district get into the very top tier schools without at least attending one of our magnet schools (assuming they grew up around here and didn’t transfer in).
I’ll take it a step further than Pizzagirl. These same public high school graduates also work alongside students who graduated from Harker, Exeter, Andover, Choate, and the like.
Imagine that.
Just about no one is going to have the drive to do well at a rigorous college unless they genuinely love learning and are internally motivated and curious.
I went to a public, average high school. I went a top 100 university after turning down a “CC’s top university”. I’ll be getting my PhD from one of the best schools in the world. My parents never checked my grades. In fact, they begged me to slow down and enjoy life. Instead, they fostered a curiosity in me that has never, ever faded. They did this by encouraging my every whim- sports, dance, science, reading, etc.
Smart, motivated kids will succeed no matter where they are. Truly. Teaching them to chase the grade rather than the love of learning will almost certainly come back to bite both of you.
It does not take attending selective high schools to get into top schools. Nor does it take creating a pressure cooker environment for kids to be outstanding students who shine uniquely amg peers. From our personal realm of experience, the most successful young adults (and by successful I mean happy, mentally healthy, and pursuing an occupation they enjoy) are those whose path has been paved by their own internal motivation, not pushed and pulled by external factors.
And to take this conversation outside the realm of CC, those same academically excellent students are not less successful academically if they do not attend tippy top colleges and universities. They didn’t “lose” their excellence by attending a lower school. The world of successful people is populated by a sea of academic backgrounds.
Thank goodness that their future lives do not rely on their academic achievements at age 12. Nor does it rely on a college application season. 
@romanigypsyeyes
I was typing when you were posting. I couldn’t agree with you more!
Hmmm…interesting comments.
@eggbeater Wondering if you’ve seen enough to let up some? I don’t know what to add other than to say that I don’t think I’ve ever seen a driven kid end up successful or happy. 6-8 is the time for them to find their own interests and if you’re driving them too hard, you end up missing the clues.
Support them. Encourage them to try some new things without being overbearing. Follow through on anything they do show an interest in. Make sure there are no things like eyesight or hearing or in-class issues that aren’t getting addressed. See if the school professionals can get involved enough to put your fears to rest.
@TV4caster Is he happy? Is he coping well when he has lower grades?
Also, how is he doing socially?