There is a Robert E Lee high school in Florida — shocking enough —
which has banned teachers and students from showing support for Black
Lives Matter.
I don't think teachers in a public high school can have the right to
teach their political views in class, giving them the authority of the
school. But they should be allowed to present their views as personal
views.
Students too should be free to show their support for a political
point, for instance with buttons, shirts, or printed handouts. (I
disapprove of making students wear uniforms.)