In fact, no child is born to deceive others, especially teachers. If he is really lying, he must have his own unknown difficulties.
Teachers should respect children and describe a child's quality as "good at cheating". Is it an irony of education?
Make friends with your child, let him know that the teacher wants to help him, make home visits, understand all aspects of your child, give him more opportunities, and let him have enough courage to face all aspects of problems.
If the child is no longer wary of the teacher, he will take the initiative to talk to the teacher.