Humor Is the Most Effective Tool
It cannot be stressed enough that humor is your most effective tool as a teacher. Humor can defuse a quickly escalating situation. It reduces tension and allows your students to see you as a real person. You don't need to be a standup comedian, nor is your job to provide entertainment. But if you can find the humor in a situation, make small jokes here and there. You will find that students will listen closer because they find your class more enjoyable.
As a teacher, you will discover that you cannot joke with all students equally. Some students respond really well to humor, and some do not. Younger children might not understand your attempts at humor at all. Therefore, it is important to size up your students and adjust your attitudes according to how they respond.
According to Jean Piaget's theory on the stages of cognitive development, most people do not reach the stage at which they can use and fully understand sarcasm until they're 12 to 18 years of age. Using sarcasm with younger students and those who have nonverbal communication problems should be avoided.
Don't Overuse It
Teachers often use sarcasm, which does have its place if appropriate. For one thing, students are so used to hearing sarcasm on television that it seems normal to them. However, if misused, sarcasm can easily hurt a student's feelings without your even being aware of it.
Make sure that a student understands your humor before joking with him. If you do use sarcasm, try to direct it at situations and not people. The misuse of sarcasm can easily lead to the perception that you really do not care about your students.