I've tried to organise visits to Coningsby and Valley, but both said that I would need an interview date at OASC after my initial interview at the AFCO.
This is basically just a filter process. The AFCO interview will filter out those with no academic potential and the OASC date will prove interest. That said, a nephew at age 15, was offered a weeks work experience with the RN. All he had to do was get himself to Gibraltar where he joined HMS Daring for the passange home.
So, if you don't ask you don't get.