Andy, we are an accredited assessment centre and have loads go through OSAT.
There is no learning involved as your 3 years experience shoud be enough to cover your knowledge requirement.
However, I have come across tilers claiming to have this experience and it turns out they haven't from their lack of knowledge and skill etc.
The assessor does all the paper work for you. You just need to do your job and thats it really!!
Give me a call here at the centre and I can answer any specific questions or clear any worries or myths you may have.
Anthony
Chase Tiling Academy