I have two expectations during the warm up. Only touch what you've been invited to touch and Look like a picture. Some kids can't read. But they know what a picture looks like. I allow them to choose between all of the activities and roam at will. If they aren't doing the activity correctly (such as sitting on the ball instead of doing the exercise), then they lose that choice for the day. If they lose two choices in a day, then they clearly can't handle making choices for themselves and I need to choose for them. Most of the time, this means I start them at one of the Fitness Circuit signs and turn on The Dinger which will ding every 30-60 seconds so they can move to the next station. Occasionally, there's the student who refuses to do anything and sometimes they have a good reason. But if it is frequently a problem, I revert to my rule of I need to know that you know. And if you can't show me you know with your actions, you can show me you know with your writing. It works wonders. With several students, I've given them a couple sheets of paper and had them write all the choices and their descriptions. Turns out, they much prefer doing the activities to writing about them.