We haven't had to go down that road quite yet. Well, not in those terms.
However, when my young son wanted to quit an activity that he had chosen to
do, I told him he made the decision and that he had to stick it out until
the end. After that, he wouldn't have to do it any longer if he so desired.
My husband and I have talked about this at length and we have both decided
that all of our children will finish what they start unless there is a
serious threat to their health (severe injury, sickness, etc.). We want
them to learn that they have to live with and make the best with their
mistakes and choices. We don't want them to learn to be quitters or that
mom and dad will always bail them out. Of course, within reason. If I were
in your position, I think (no matter how hard it would be to see my kid get
bad grades and suffer - trust me, I am one of those that was SUPER
competitive in school and get woozy just thinking of my child getting a bad
grade) I would tell him to complete the year. Learn how to study and work
hard and do what you set out to accomplish in the first place. After all,
you did give him fair warning the year prior.