Encouraging the positive behaviour

We as a teachers sometime make a common mistake; When there is a disruption or interrumption during the class, we tend to call on the kid who is not doing the right thing. With this observation, I have learnt that kids imitate a lot, and if we always tend to call on the person who is doing the bad thing, the other kids are more likely to imitate that  bad behaviour because they want the teacher to notice them, and the class would become a mess. Kids who do the right thing could even start to feel that it is not woth it to do something good because no one notices it, and as a teacher that's the last thing we want to happen.
How nice it is when the teacher only focuses on the good behaviour and congratalates kids for that, because kids will often want to do the right thing and even if there is one single studying misbehaving, he or she will eventually want to do the right thing to when they see others making good choices.