Rather than criticizing unwanted behavior or answers, reward correct behavior and answers. Remember that adults and children alike continue or repeat behavior that is rewarded. Small children can be given a balloon, a piece of gum, or a set of crayons. Even at the college level, many professors at various colleges have given books, lunches, certificates, exemptions from final exams, verbal praise, and so on for good performance. And the important point is that extrinsic motivators can, over a brief period of time, produce intrinsic motivation.
Students respond with interest and motivation to teachers who appear to be human and caring.
Teachers can help produce these feelings by sharing parts of themselves with students, especially little stories of problems and mistakes they made, either as children or even recently. Young people are also quite insecure, and they secretly welcome the admission by adults that insecurity and error are common to everyone. It is also a good idea to be approachable personally. Show that you care about your students by asking about their concerns and goals. Such a teacher will be trusted and respected more than one who is all business.