How To Participate In Reginal Chess Tournments

@madhulika78 , the easiest way to find regional events for juniors is to contact the US Chess Federation (USCF).
See here. At the bottom of the page, it says: "We encourage you to contact us if you don't find what you are looking for here, or if we can be of assistance to you in any way." This applies to you!

In the meantime, he can play online. See Chessbase for resources.
Also here: Fritz.
I don't know what his level is, but he may benefit from these problem books. The first is the one I give kids interested in chess. It is very enjoyable!
Beginner's Chess
Chess: 5334 Problems, Combinations and Games

 

@madhulika78 i dont have a clue about how it works in the us.
but one place your kid could learn is
Play Online Chess Tournaments - Chess.com

2017 US Chess Championships - Chess Forums - Chess.com

there are loads of online competitions hat happen to keep working on strategies. and yes you have chess forums country wise and @sokanasanah has already given us one

if possible downloads old games and they were available at chess.com.

 

For ELO ratings, see here and here.
Chess.com will also help with ELO ratings and online games with real opponents, as shanvy pointed out above.
However, before entering into the ranking calculations, make sure he is mature enough to use it to improve his skill at the game. It would be counter-productive if he gets bogged down in an "I'm not good enough" mindset. You need to pay attention to his personality and maturity level. Guidance from the school chess coach will help in approaching scores with the right frame of mind. There is a life-lesson to be learned here!

This is a teaching moment! Ask your son to email the USCF**. He can draft a note in consultation with his local coach - a brief description of his interest, participation and progress so far, followed by a question about what opportunities exist in your neighborhood/town/state for advancement. When an enthusiastic kid writes, people usually respond!

**I assume you live in the US since you mentioned "school district" - that's a very American formulation!