Hey M.:
My son is now 14-1/2 and has special needs, so I speak from experience that began when he was 2-1/2 with his first evaluation with Child Development Services.
If you as his parent believe that he still has the need for OT then stick with it. You are his BEST avocate and know him the better than anyone. No degree or amount of time will ever change that.
You will be suprised from the psy eval, or at least I was when my son has his 2 years ago. I only wish it was done sooner. In any event, it's a baseline that can be use for comparision in the future and if you're lucky, you won't have to use it for any comparision.
PLEASE DO NOT do the "wait and see" game that the professional and schools will want you to do. Proactive is always better than reactive especialy with your child and how he will learn.
So...stick with what you think is right no matter what the "professionals" say, continue to study up on all issues as you have (Great job, by the way !!) and you go girl !!
It's a trip but one that empowers you as it is all about your child, his education, how he learns and not only making sure he is "not left behind" but that he is successful and confident.
God speed.
Smiles-
-W.