Do not forget that the aircraft is not the only threat during stall practice. I know of at least three instructors who have had a student lock up on the controls with full back pressure during stall practice and lost 1000-2000 feet during the recovery. One of these was in a PA28 which suprised the student with a wing drop in a straight and level power off stall.
Whilst a straight and level stall may not constitute an aerobatic manuevre it can very quickly turn into one without much warning when inexperienced pilots are involved.