You can only sue the school if--1 There were prior racist comments or acts by this teacher which the school was aware of but, despite being aware of them, the school did nothing to reassign, discipline, provide sensitivity training for, etc. the teacher--that is, the school allowed his/her racism to continue or2 You report this comment to school administration, but they do nothing--not even investigate in a meaningful way--and you suffer future racism by this teacher.That is, the school would only be liable if they fail to take action against racism an employer is not liable for an isolated racist incident, because the employer cannot prevent isolated bad acts. Rather, the employer responsibility is to provide effective responses to racist acts when they occur and have a useful policy against racism.You cannot sue the teacher, because individuals are allowed to be racist the law does not litigate opinions.