for my 13 and under crowd, i want to see them sweating but not dropping like flies. if you get them past the lethargic nintendo mindset they tend to start smiling more and putting out greater effort. at our studio, i'll call 'sweat check!' during a workout and then tousle a student or two's hair. if it's not at least damp, we pick it up a notch.
for the teens and adults, we push pretty hard during a workout class. not every class, mind, but at least once a week. the key at that age is to help us remember that we're capable of being more than we are. so we'll go until the students in poorer shape start to miss a beat or two and until the better conditioned students are starting to sweat.
older adults attend the same classes, but they understand that they're to choose what they want to do and to modify the workouts to suit their needs. actually, that's true of most students, but i give the older adults the most leeway. first, they're my seniors and i feel funny telling them what to do. second, it's not appropriate to push so hard over forty -- they know their bodies by then and can make better decisions than i can about how hard to work.
also important to remember who you're dealing with. some students are simply capable of more than others today. tomorrow that will be different, but i'll tailor the day's workout based on class attendance.