My son is almost 10 and also developed his own 'sense of style' around age 6. He likes a rocker/skater look as well, but will usually get dressed up when I ask him to. It's a GOOD thing for him to be developing his own personality and sense of self. We had a few talks about different occasions and what was comfortable and appropriate for one thing, might mean wearing something different for another.
What has worked for me was really working to find 'dressy' items that we could both agree on. My son wouldn't be caught dead in a polo button down- lol, he just says that isn't the way he wants to look!
But a compromise of khaki pants with a button down shirt that has a guitar screen printed onto the side and a navy blue suit jacket (couldn't even see the guitar, lol) went over just fine!
He also loves the Lands End moc shoes for boys. He has a tan pair for 'dressing up' and a blue pair for everyday at school. They are pretty affordable, look nice and last really well- we hand them on to a friend for her son when my son outgrows them.
This will take a little more effort on your part than a trip to Walmart or something. I don't allow my son to wear anything tacky looking or shirts with inappropriate sayings etc. I can't stand those- so he knows they are out and doesn't even ask. But a retro Star Wars shirt or one with a cool guitar or drum set on it is cool.
There are a lot of sources online for cool rocker/skater type clothes that are not really any more expensive than what you get at the store- you just have to search them out.
My mom actually found the guitar shirt I mentioned above online at Red21. Their prices are a little expensive (that shirt was a grandma present) but it is really just an oxford cloth shirt, with a print screened onto it- it is cool looking but also kind of dressy, so it was a good compromise.
If my son sees something he really likes from an expensive company like GuessKids at a department store, we wait until it has been marked down- I am always willing to look for things in his style, but I don't compromise MY price point for him! He knows if he wants it, he may have to wait until it is on sale.
We also make deal occasionally- something I want that he agrees to wear for a dinner or something and I'll throw in a cool t shirt or something else HE really wants to wear to school. He does not really care about 'labels' or brand names- it is all about 'does it look like me' to him.
Combine things from Old Navy, the Gap sale rack, Target and department stores and online and you can get a cool look that is dressy enough for you, but skater enough for your little guy!
As far as anyone saying this is a 'respect' issue. My son is VERY respectful to me, teachers, etc. He gets excellent grades and, if anything, is not 'following the crowd'. He's never watched the Jonas Brothers or any of those other obnoxious 'tween' shows on Disney or Nickolodian and isn't copying something he doesn't understand.
Talk with your son, if you are concerned that he is just trying to copy someone on TV. Talk about WHY he wants to dress a certain way. Someone like Tony Hawk has been very successful doing what he loves and teaching others to do it and can be a better role model than a lot of people kids look up to these days.
Don't make this into an issue it isn't- your son is not being disrespectful simply by wanting to dress a certain way. My son would be the first to say that I am a strict mom and he gets disciplined when needed- but respect is a two way street. We respect one another and trust one another. It's really rude for the poster below to suggest that he would dress a certain way just to show disrespect. Let him be true to himself - don't make him a sheep who only learns to go along with what all the other kids dress like and say and think!!