When I fly with a student who has flown with another instructor, I let them stick to their standard procedures as long as they are safe. The key areas are things like use of carb heat, and touch and go technique (to put on power first or raise flap). By hopping from one instructor to another early on you get told contrasting things each lesson, and are too inexperienced to make your own mind up about what is the right thing.
One continues to get this after one has a PPL with check rides. It's extremely annoying and frustrating. I suspect instructors generally are just too inexperienced / too immature and opinionated to take a more objective approach.
I was chatting to a student recently who was very upset because his instructor (different to his previous lesson) had bawled him out for not being properly prepared. One of his crimes was that he forgot his checklist at home. Please - just lend him another, for goodness sake!
The student was so upset after the briefing that he didn't want to do the flying part of the lesson - which meant the instructor received nothing.
Flying schools really need to become more professional and stop acting as if we were still in the early days of flying. There are just too many stories from upset students. Ok - it might be partly the student's attitude - but then not many students come away from an art or language lesson feeling like this. It's pathetic.