substitute teachers

I feel bad for the substitute teachers because kids behave different when their teacher is here, but when their teachers wasn't near them, they act differernt. For example, in my class, when my teacher isn't here, we have a sub, and some kids likes to drive the subs crazy. They don't treat the subs the way they treat their teacher, and that always makes the sub have a hard time dealing with them. Also, when kids didn't see their teacher around them, they would chat with their friends and maybe even ignore the sub. However, when they know that their teacher is watching them,then, they wouldn't talk with their friends or ignore the sub. I think being a substitute teacher must be very hard.