Is studying harder levels

As most of you do, Korean students usually do work of the grades ahead. however, is this really good? Our parents tell us that if we learn one time at academies and again at school, we would understand completely. Many people believe this so 5th grade student s doing middle school math is a very common, and almost normal thing to see. However, I personally think that this is not a good type of education. I believe we should simply follow how the school teaches. This is since, if we know everything already, we would be bored and we won't really like to be in class. We will seem like a bolt went lose in our heads and we won't listen since we already know everything. And also, the reason that we have elementry, middle, and high schools are separated is to match our skills to our grade. But learning new facts that you are not ready for would be hard and you will feel stress. We should all just learn what is our level I don't think it is necessary to learn stuff that are grades in front of us.