With regard to the OP on my very first trial lesson, I was allowed to fly straight and level and try a few turns etc., but when we were about five miles out on our return, ATC asked us to stay out of the way as there was a 737 coming in. The instructor took control and carried out the instruction (as I would have expected). This was my first lesson after all and I not am sure that I fully heard/understood the ATC instruction anyway. Most of these "trial lessons" are bimbles to see if the potential student likes small aircraft flying rather than a lesson as such.