about 自信心

Two days ago I got a school letter about he will get a "c" if he doesn't turn in his AP computer homework. I talk to him that if he get a "c", he will be disquilified for this class and we will give him time out for his hochey. My son said " I am very good at class and this teacher will never disquilify me". then he add that "I am your son and you should know me better and I will talk to my teacher to correct this error". Acturally this whole thing is just a misunderstanding about which version of compeller the students should use. Here I see my son's 自信心.