Try to understand the reason for his dismal performance in Maths.
Is it due to dislike for the subject or is it an aversion to the tuition class? There may be other reasons beyond this, you are the only person who can find this and help him.
The rhetoric of “study hard, must get good marks”, may not work well with the child. Spent time with him daily, do or talk things that he likes.
In a few days, you will find the problem and eventually you will find the best solution.
All the best.
PS: Matters like this are discussed in the FORUM and usually not in ASKQ. You can post it there, you may get more refined reply.