So many students coming out of high school think grades are pointless, that I have to do as much as possible to encourage them to recognize the importance of grades. I think it is easier to teach highly-motivated people without using grades (which is how Continuing Education works), but a school has a responsibility to evaluate students so that employers can have an additional way to choose between them. The following illustrates that.
Someone tells me that about 15 years ago, my school fell victim to one of the "education experts" who have gradually ruined K12 schools. This "expert" (who likely never taught at this level) said that if a student wasn't getting an A, it was the fault of the school for not doing the right things. The school swallowed this foolishness, and one year the only grade anyone received was an "A".
When employers found out about this, they came to the school and said they would no longer consider our graduates for jobs. They couldn't tell who had done a good job in school and who had not, because all the grades were A. They wanted the school to give grades that reflected actual achievement.
And the school changed back to the standard way of doing things.
My wife, who hired many, many people when she was chief librarian at Methodist College (17 years), definitely paid attention to grades. I tried to when I hired people. If you aren't doing well in school, why would you be expected to do a good job in the real world? In a sense, school is a job internship for the student.
Getting a good grade requires effort (and capability) from the student. The teacher can only give the opportunity, he or she cannot be a magic pill that enables you to learn without effort (Matrix-style). It may be easier for some people than others, but a student has to EARN an A, or earn a B. A "C" is not "average", it's a poor grade, in most schools. Heck, it's flunking in graduate school.