I do want to say one other thing: Make sure you remember your place. The way many of the teachers talk on here, you'd think the students have to take lessons from them, they have to be paid, they are entitled because they are the teacher and may do as they please. No. The student does not have to take lessons from you, and if a student is not having fun and does not see progress, he/she can and should stop taking lessons from you. This is not to frighten you, but many people don't realize that although they are being paid for something, they don't have to be. They take advantage of the idea many parents have that piano lessons are good for children and therefore they must have their children take lessons and make them practice. It probably carries over from compulsory education, where if you don't like your math teacher, too bad, suck it up.
Each student is an individual and learns in their own way. It some cases of bad students, it may be that the student simply does not want to take lessons and resents the parents' rule over them. In most cases, though, I'd bet uncooperative students are bored, confused, impatient, amongst a host of other things. However, when students are having fun, the boredom and impatience will ease. You are a teacher, yes, but you are not a disciplinarian, nor should you be force-feeding them unappetizing literature and furthering the idea that piano is dull and not something they should be concerned with. Bottom line, you are being paid to teach the student, therefore, you must adapt your teaching to the student's needs and desires. It takes a little effort, but it is possible to achieve both your ends and the student's. We talk about the business side of teaching when we talk about payment, but we don't consider that as our customers our students should decide what they are purchasing. If the student wants to learn popular music, you'd best be teaching them popular music. Yes, people will get mad at me for saying it. "If I just let my students pick what they wanted to play, we'd never get anything done!" and blah blah blah. It's not about you, or what you think is best for the student to learn. You know what? A funny thing happens when you work with kids on something they want to play. They progress faster, have fun, and practice during the week. Huh! Your job is simply to guide them through the learning process, and prevent them from doing anything which could cause harm (much harder than it sounds).