[Jean-Paul]

Just watch them. You're over complicating things. If someone is struggling, quietly go tell them they're doing great, and to let up a little. I have a pretty wide variation in my classes. I just make the class meet them where they are. My advanced guys can crank up the spin bike station a couple more notches, jump a little higher, run out with bands a little faster, do the slide board at a wider setting.

All you have to do is have a well laid-out workout, warm them up well, be confident, be supportive, be attentive, and don't let them see you doubt yourself. Smile a lot and make their workout the most fun they've ever had.

I usually set a minute to perform at given number of reps with 30 seconds to switch to the next station. Someone just getting started may only have 2 circuits in them, then I'll tell them to stop and the advanced people will go another round.