My son is 6th grader and 5'5''. His birthday is Sept and is oldest in his grade. So he looks relatively tall among his peers.

He can handle the ball really well and has the speed with good defense. He plays better as a guard. Genetics tells me that he can only play a guard in high school and won't grow beyond 6 feet. So I will continue let him focus on fundemntals such as ball handling, speed, defense etc.


But whichever team he plays, he stands out as tall yet not the tallest. Coach will put him to do 3 or 4 (sometimes 5) because there are many other little guys who can't play any other position except guards. He ends up doing terribly though trying hard.
Nobody teaches how to play positions 3 or 4 at all. He ends up lost and doesn't know how to get open or score, leaving bad impression to coaches. These days, no coach has patience for potential and a player needs to contribute immediately.

can anyone point me some good video drills for positions 3 or 4? Though I am going to make sure he continues to improve his guard skills, I want him to learn some sills playing 3 or 4 to survive for now. Otherwise, he looks horrible playing those positions offensively.

I wouldn't honestly worry about the numbering of the position. Worry about the skills.

Is he playing outside? Is he playing inside? Is he swinging between the two positions?

Regardless of what he is doing, he will need to be good to develop his skills at

on offense:
pivoting
shooting
ball-handling and driving
passing

Defense:
Stance and positioning for on-ball defense/footwork.
Knowledge of one pass and two passes away positioning and off the ball defense.

At a young age, don't sweat his learning to play a position. Just worry about him learning how to play. I'd focus on more perimeter oriented skills and pivoting. The pivots he needs to use can be used away from the basket to break himself open, or close to the basket as post moves.

Check some of Don Kelbick's materials, as I think the development of good footwork will help him regardless of where he plays (close to the basket or away). You want a well rounded player developed at this age, and not worry about anything position specific.

Brian has some excellent points, the footwork is a pretty big deal and knowing how to pivot correctly is something that should be used at all positions. I'm big on Mikan drills for all players, but especially for big guys, adding two ball mikans and reverse mikans. You have to be able to go left or right when executing a finishing move.

Interesting that your son finds himself being tagged as the "big guy". Same thing happened to my son and it can look awkward when a coach tells you to "go post up" and you have no clue what to do. Addressing the 3 and 4 slots is a bit tough without knowing what kind of offense a team is running. At the 6th grade level, I found that the 5 position had more definition than any of the other positions. If your son ends up playing against the other teams big, he'll need to know how to defend a big.

Not sure I'd get too hung up on this stuff, but maybe you can pick out a few simple things from the vids below that might help your son. I really like the vid on defending a post player. I've found that most players don't really know how to effectively defend their opponent when they're close to the basket. Not just big on big either.

One of the better videos I've found on defending the post or really anyone trying to post up.
https://www.youtube.com/watch?v=6JvsNiOGG6I

A good video on some basics of posting up and post moves:
https://www.youtube.com/watch?v=mA7TvmTZfH4

Drop step video:
https://www.youtube.com/watch?v=4bndda2KIVA

EDIT: If your son isn't stuck posting up and finds himself not out top, one thing that will probably help is setting good screens. Learning how to roll after setting an on ball pick. Again though, at the 6th level, this is a good skill for any position to master.

Thank you for all the tips. I wanted to make sure he can do all positions.
When he is PG or shooting guard, he would score half or 1/3 for the team. When he is put to do 3, 4, he doesn't know what to do. He either stand at near the baseline/three point line or running /trying to get open (but can't get open). so he doesn't get the ball that much. basically he would look like worst player on the team. but he would probably beat everyone else 1on1 in the team.

I can show him videos on post moves. But I'm guessing getting open and know where to go is the biggest problem for him when playing 3 and 4. He knows what to do with playing 1 and 2.

I think what you're talking about here is learning how to move without the ball and get open. For example, knowing when you're being overplayed and making a back cut. Some of this comes as kids play more, they gain more "court sense" and begin to see what works when they don't have the ball.

I'd be real surprised though if a coach doesn't lay out some type of basic offense with guidelines. Otherwise, kids will be cutting at the same time, the floor will be unbalanced, etc.

Here's a link that might help:
https://www.breakthroughbasketball.com/offense/cutting-moving-without-ball.html