Your take appreciated - Pre-School or Kindergarden for 4 yr old?

My son is 3.5 yr old. His reading and math levels are already at kindergarden level. He knows a lot of words and can read some books by himself and can count to 100 and do some basic additions. He speaks both chinese and english very well.

We have been trying to enroll him in the pre-K class in a very good private nursery school. The school headmaster interviewed him a few days ago, which was an eye opening experience itself. After spending an hour with him, the headmaster suggested us to put him in the school's kindergarden class, a level above the pre-K. Next year, we would have a choice to put him either in kindergarden or directly to 1st grade in our public school system.

My son was born close to the birthday cut off date in our school district. He would be already the youngest one in his class if he follows the enrollment calendar. He is socially and mentally mature enough for his age group.

I am concerned about future implications if I put him in the kindergarden class now. Anyone could care to share their take if you were in my shoes? Many thanks!