You need to figure out if the comment the teacher makes is too forceful, or if it is a small comment that builds in the child’s mind. When my daughter was 13, you could say a dozen nice things about her, and somewhere in there have a quick, unemphasized criticism about her shoes not matching her dress, and that will be all she would focus on. It would grow in her mind to the point that I practically assaulted her with the fashion police.