Addressing "Racist" Teachers

In my setting I spend a lot of time with "struggling" kids.  I'm more of an at-school parent or mentor than a teacher.  Every day I review students' grades with them, help them understand what needs to happen to bring them up if necessary, and try to help them reflect on the choices they make so they can see the consequences more clearly.  I often hear a variety of excuses from students for their low grades or repeated behavior referrals, and the one that I hear most often is, "That teacher doesn't like me."  It usually isn't true, of course, but it feels like reality to some of those students.  When I ask the kids why they think that I hear all kinds of reasons - "She gave me lunch detention," "She called my mama," "I turned that paper in and she didn't give me credit" - things like that.  Unfortunately, I also occasionally hear from my students the opinion that certain teachers are racist.  And sometimes, I see where the kids are coming from with those remarks.

I have heard colleagues share some nasty opinions about some of their students.  In those comments race is never mentioned, though it is always implied.  With other colleagues, I have never heard anything offensive come out of their mouths, but the expectations they have for their students and their responses to the students' behaviors make it clear to me that race is a divisive issue in their classrooms.  I may be one of the few teachers on campus who has the opportunity to make such observations due to the nature of my role, and I often struggle with how to respond to my colleagues when students point out that race is an issue with those teachers.  I am curious to hear how other professionals would approach a colleague, if they would at all, when they hear students describing that teacher as "racist."  Please share your thoughts.  Thanks!