Balham Bob
The physics part of OAT's assessment consists of 15 timed questions. The maths part has 24 questions (I think) which again is timed.
Nothing particularly difficult - long division/multiplication, changing subject of formulae etc. For the physics you should cover electrics, magnetism, kinetics, light & energy.
The sim check is the fun part. When I took my sim check, it was a current Captain for DHL cargo that did it. Fine chap he was and it was very relaxed. You were asked to do banking, climb/descending and constant speed/altitude & heading tasks.