I have a child with a cognitive disorder and she didn't speak until age 2. We were right where you are now and i know from experience that if you try and push the child they will just shut down and do nothing. Why is the ABA involved. The only ones that were involved were the speech therapist and my peds dr. They have worked so many miracles and i heard mommy for the first time when she was 2 and now she is 7 and is a talker. She still has alot that she still cant say good but she will get there. Just do what a parent would normally do and be patient and supportive and everything will be fine.
I agree with Dr. Kennedy about not forcing him to speak. The age at which a child of normal intelligence begins talking can vary greatly. My husband and I both come from large families, so there are children, grandchildren and cousins all over the place. Two of the children did not speak until they were three. They were completely normal. I believe that Einstein did not speak until he was four.
Try working with him with Speechtails.com. I have had really good success with it with my daycare children. It is fun and has increased their vocab. It is so hard when you have all these issues at the same time. Good Luck
It is not useful for you to pressure your son to talk - that will actually work against what you are trying to acheive. Why is the ABA person involved? Does your son carry a diagnosis along the Pervasive Developmental Disorder continuum?