Hi Kelly,
I agree with some of the other respondants, his height really isn't a factor(it will probably be an advantage). My daughter's birthday is a little later than your son's(Nov) and we put her in "begindergarten" instead of kindergarten. Cognitively, she was more than ready, but she had only spent a few months in a structured setting, and wasn't ready for kindergarten in that respect. It was the BEST decision for her. The curriculum is the same, just at a slower pace, and usually there is another adult to help out. She excelled, and has continued to excell. She is now in the fourth grade, and continues to be an all A student, and classroom leader. That extra year helped her to gain maturity and confidence. And there are always several other kids in her class with fall birthdays (who are the same age as her), so she doesn't stand out. Personally, I feel that when she reaches Middle & High School, her extra maturity will only help her to make better choices, and resist negative peer pressure. I know that this is a very personal decision, and I hope that you find the advice you need. Good luck