In a mat work class, all participants do the same exercise as determined by the teacher. There may be small variations to an exercise to accommodate more able people but generally everyone does the same thing. The class size is usually determined by the size of the room and by the teacher. Typically, class sizes can be between four and twelve.
Using Pilates equipment is a more intense experience as you are being taught on an individual basis and using, for example, the Reformer and Stability Chair. Resistance is added to make the exercises easier or more challenging depending on what the goal is.