Nobody should get expelled for bad grades. If anything the principal or him/her teacher would just talk to them and see what would help them get better grades. I am a teacher myself and I have never heard of any school that expelled their students for bad grades. In my opinion, if your child gets expelled for getting bad grades, ask the principal why he/she got expelled and I am 99% sure that he/she would be very willing to tell you. Your principal should show the parents him/her grades. If the principal even said that this particular student got expelled for bad grades, I would sue the school or district. In our district, it is not acceptable for a student to be expelled for getting bad grades.