If a witness to a crime at school has goten introuble is he considerd void?

ok recently a Friend of mine had gotten punched by a high school kid at my middle school i saw and talked to the kid before he left. (he was walking away from my Friend) he did verbally confirm punching my Friend and he also confirmed he did it without cause. three weeks later when i was called in as a witness what i said was considered irrelevant and was not put on the record because i had gotten in trouble at my school before. now my friend has gotten in trouble because no one confirmed he didn't provoke the high school kid. can the school do that? (please i need a source, california law/penal code, or a past court case showing what the outcome was.)