I do not think that I would take any novice rider for five arena lessons a week.
My belief and experience says that once a rider is reasonably confident, has balance and can keep their hands steady then go out and about for lessons, using a lead rein if necessary.
Talk about all sorts of things, the trees, films, whatever so that the learner relaxes, gets the feel of the natural movement without having to worry about bending the horses around the corners of an arena. In relaxing their balance will improve and with that their seat. They get a sample of what riding is about - going on trails, seeing views and just the pleasure of being with a horse.
I do not nag them to keep their heels jammed down or sit tall with a hollow back, I let them find their most comfortable position, improvements can come later.