Well I yell sometimes but only when I know the student knows better and is acting stupid. We follow a set syllabus as part 141 school, the student has a copy and the instructor, both the student and the instructor know exactly what is expected of them every class and what the next day lesson will be. I find this the best way to go about things. If I have to repeat a lesson with a student, I tell them exactly why, I point to the completion standards and explain to them they did not meet the requirements.
I've never had a student disagree with me on how they did, they know they did bad and feel angry at themselves.
You having to fire your instructor, that also makes me laugh, lol. I have people constantly bugging me to be their instructor, there just is not enough room on my schedule or time in a day to get everyone done. Did I mention I am the only MEI at my flight school? Life is good...