I don’t know what other answer there is to stop teachers getting away with this shit. The racism and sexual harassment I saw on display when I was going to school in Indiana in the 80s and 90s was not a secret. But since it was always the teacher’s word against the kid’s, the teacher always got away with it. The only time I can think of that it didn’t happen was when a very devoted girl and her family in my high school spent a lot of time and money in court suing a teacher who sexually harassed her in middle school. He had his job the whole time (he was finally fired when he lost the case).