Yes, it's my fault your kid never took advantage of the retests I offered and posted online.
It's my fault your kid didn't know about the extra credit that I announced in class and posted online.
When you say that I refuse to help your daughter but help other kids, what can I say? You have made up your mind. Everything I tell you is a lie. Your daughter is perfect. I shouldn't have counted those questions wrong when she choose to leave them blank. I shouldn't have given a reading check quiz. I shouldn't have assumed your daughter read those five pages I assigned. I should not expect her to open the notebook and find the answer on the handout I gave her. I should not have told her to try something on her own before I just handed her the answer. I should not have told her that she should use a dictionary when the question was for her to define a word.
Yes, it's my fault your daughter has a C. I'm the person who made the decision decades ago that makes an 82 a C. I'm the mathematician who randomly decided that math is math & numbers average the way they do.