Aside from the above excellent answers, I sometimes throw in circuit style classes. Each participant will work at their own pace, but they need you to stress that they should work out at their own appropriate level. Take this example: I may have everyone cross the floor and do 10 wall push-ups, and then cross to the other side and do 9 wall push-ups, (and on down to 1 push-up). This is a mix of strength and cardio. While my ‘spring chickens’ will sprint from side to side and do their push-ups on the floor, my ‘seasoned vets’ will stroll more slowly, and use the wall for push-ups. Those done early are doing squats until the rest catch up. Everybody works at their own level.
Circuits with stations set up around the room are another way to let everyone work at their own pace, rather than a fast paced, choreography laden class that will leave a few behind, never to darken your door again.
Successfully teaching to multi-levels (both fitness & skill levels) is the biggest challenge and most important aspect of teaching group exercise. In two words:
Progressions and Options!
Whether I’m teaching a core conditioning class or a choreographed step class it’s the same: I start with a base movement that everyone can do, and progress it with optional variations to make it more challenging and/or interesting. Encourage & emphasize the importance of staying with whatever part of the progression challenges them *enough*.
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.