Let him practice every day. If he fails, he will fail every time. Then all you have to do is help him do his homework correctly and understand the topics in the book. I also taught math in college, and my children got poor grades. I used method 2 to help him build confidence, and then helped him review the previous content. He made rapid progress in his grades, but his parents were too stingy to let me drop out of school in one semester.