This question usually comes up after a teacher tells a child’s parents that the child is not keeping up with their schoolwork. Often, the teacher actually suggests that the child repeat a year.
However, although the indication given is academic, the problem is most often emotional.
If the reason for the child’s poor performance is academic, I believe there is no point repeating a year. If there is a real difficulty, time is not the cure!
It is better to offer special support to the child during and after school, or in extreme cases, in a special school.