Acting out in school - Lesson incomplete

The title is something all kids do. The reasons maybe different, but it happens. Have you ever questioned an eight year old boy about why he is misbehaving in school? I have. The answers are many if you keep asking just to find that one answer you want to hear. The answer I got that stood out was; my daddy told me I don't have to take any mess from the other kids in school. I understand that may have been the answer to something that had happen in the past, but does it relate to what is happening now. I ask what was going on in school when his dad told him he didn't have to take any mess from other kids. His answer was: someone had tried to take his money and he gave it up because he didn't want to get in any trouble for fighting in school. This is when his dad told him not to fight unless someone tries to hurt you. This didn't apply to when someone is making fun of you and laughting at you. So the lesson was incomplete. The answer didn't apply to all situations and now dad isn't there to point this out. Is this how mistakes will happen in his life? Will unanswered questions to incompleted lessons be the cause of a good kid being misunderstood?