I didn't answer your question about what I would do. I am a upfront person, especially when it comes to paying thousands of dollars for school. I would pull your teacher aside and explain to them how you feel and how it is very offending when they degrade you. They should have bedside manner if they are working in the health field.
I am a little more than halfway done with my LPN program and I understand what you are saying about not retaining anything. LPN programs now a days are designed to stuff you full of information in a very short period of time. I make myself a to do list every week. I write down homework and even schedule times to study. This has helped me stay organized and calm. Some of my classmates and I have also put together a study group which is so helpful. Have you tried talking to anyone about your teachers? I would definitely go to a Counselor or student advisor. Remember that when you graduate it will be the best feeling in the world! Because you overcame all of this. You will be a great nurse because you are learning how to deal with difficult teachers as you will patients. Hang in there! The end result is completely rewarding!