Being honest with your students and speaking to them with an honest concern for their well being is a powerful tool in dealing with a problem student.
Of course it depends on what the problem is. There is always the chance that you have the rare problem student who's goal is to be a problem and who is not in school to learn anything, they are just there to see what kind of trouble they can cause for all and sundry. For that kind of problem student all you can do is your best and then wash your hands.
