I teach an all levels boot camp! You have to modify, modify, and modify some more! Focus on form. I always tell my clients…it isn’t practice that makes perfect…it is perfect practice that makes perfect. You plan your classes with all people in mind. Offer up different alternatives. In my case we focus on the basic moves in almost every class so eventually people might not have to modify (for example I might have a new member work on learning a good form squat not going to deep, while I have my more advanced clients doing deep squat kicks or squat jumps). I also use the rest based exercise principle in my classes. We go for 2 minutes on most exercise but my clients know that within that two minutes they are to go for as long as they can, rest for just a moment, and go some more. By giving them the option to rest they don’t feel like they cant do it! My classes are HARD and yet I have all fitness levels that can squat, lunge, do push ups like no bodies business LOL.