Irresponsible teacher? Two Q's about grades?

Meet up with your teacher with your report card and tell him to explain step by step of how he arrived with your current grade. Then explain to him that you had participated him group discussion and scored well on a major test. Ask him to explain why he had given you a zero percent on participation when you had participated. If he still wouldn't change it. Then he must have something against you. Take it to the school administration and explain it to them. I would get really mad if one of my teachers did this to me.