For those children who can't get into high school, repeating is a better suggestion. It may be a bit difficult to get into a key high school, but the threshold of a regular high school is not that high. As long as we put all our energy into our studies, the vast majority of us have what it takes to get into a regular high school.
The past three years of middle school, as long as not too playful, can have some knowledge gain. In the time of repetition, we target those weaker subjects for remedial reinforcement. Force yourself to do more questions, ask more teachers, so that repeat a year down, will receive the desired effect.