Grade 7, is it really needed?..

I am from the province, and I’m not familiar with a grade school having seven levels. All I know is that grade school us just up to six levels. So to my surprise when I entered college, some of the people in my batch are way older than me. And that’s when I found out that some schools require grade seven to their students before they can graduate from grade school. And I just think that it is not really needed because I graduated and got accepted in DLSU without me taking grade seven. So what is grade seven for? What advantages do students have who took grade seven to those who did not?