Teacher here.
Your child's success depends mainly on three things: the child's will, the parent's support, and the teacher's skill. If your child doesn't want to learn, he won't learn. If you don't f**king feed your child properly, he won't be able to learn. If your child gets his way at home, he will be a terror in class and won't succeed.
I am only a part of your child's education. I can't do anything if he refuses to learn or if you refuse to support him.