Whether it was the fifth-year O.W.L.s or the seventh-year N.E.W.T.s exams, they were of paramount importance to young wizards, the school, and indeed the entire wizarding world.
To put it more plainly, the O.W.Ls were essentially middle school graduation exams, passing which earned one a middle school diploma. The N.E.W.T.s were high school graduation exams, passing which earned one a high school diploma.
Only with a diploma could one prove their abilities, land a good job, and earn more Galleons in the future.
Chapter 123