My son is going through the diagnosis stage

Hi all, I'm kinda at a cross road. My son is nearly 4 and starts reception in September. I've known for a long time that my sons behaviour is different from other children his age. His always been very advanced but his emotional and social development is not progressing at the same pace. His social interactions can be very aggressive and controlling towards  both adults and children. He is awaiting a CDAC assessment but I'm not quite sure what this is and what it covers? I've been doing research and I think he may be HFA or aspergic, is there anyone else who's going through or has been through this already?  Any advice would be brilliant as I really don't no what else to do right now.