At what point in AIT for 68W do you choose or get igned a specialization area?

I'm going in the Army in Oct and my AIT is scheduled for Jan. I will be a 68W. At what point in the 16wk training do you find out what specialization area you will go into. Such as Occupational Therapy, Flight Medic, Physical Therapy, and so forth. Does is go by how high your scores are?