Martingale collars (also called limited-slip collars) are usually made of flat nylon with a smaller fixed-length section (made of either nylon or a short length of chain) that, when pulled on by the leash, shortens up tightening the collar around the dog's neck, to a limited extent. When properly fitted, martingales are looser than flat-buckle collars when not tightened, and less severely corrective than slip collars when tightened.
A training class is not there to train your dog. Its purpose is to teach you to train your dog so you will need to be committed to train your dog for short sessions (5 minutes) several times a day rather than just simply turn up for classes! This little bit of training everyday will be repaid with a lifetime of living with a well behaved dog. You will also learn to avoid problems before they begin as well as receive help to overcome any that you already have with your dog.