Source
Having good grades isn't enough to tag one as being intelligent, you can have good grades and still not be intelligent enough as people think you would.
I say this based on our current educational system, don't get me wrong but if we are to talk about good grades with how our educational system is currently then the Grades doesn't COUNt at all, because most students even go as far as buying their results and even cheat just for the grades without having any educational intelligence, but just for the grades.
So when one is said to be intelligent it means the person is clever and to be clever you have to be smart, quick, sharp, skillful, creative, these are some major factors that makes a person intelligent.
Just having good grades and not being skillful or smart enough to handle some other general or social activities doesn't qualify one to be a full package of intelligence.
It's necessary to go to school, very necessary but I wouldn't say it's compulsory. I say this because within the four corners of the school is not actually the only place one can aquire knowledge.
Education is also not completely useless but then education doesn't really ensure that one is also intelligent. Though going to school can make one more academically intelligent, but it's still not enough to say one is generally intelligent.
So there's a possibility of one becoming smart without actually being within the four walls of a school.
We can now say schooling helps one acquire some needed experience or knowledge, but there's a huge possibility of one becoming smart without actually being within the four walls of a school, there are other ways to prove to be intelligent without schooling.
Everyone wants to be seen as a smart or intelligent one, then they try to do things that qualifies them to be intelligent, like hanging out with the smart ones there's a saying that birds of the same feathers flock together so when they hang out with the smart one they are also seen as being smart too.
So aside from going to School one can also acquire knowledge by reading books, making research online, asking questions. Then also having self determination, knowing what you want and going for it without getting distracted by some certain factors like family, friends, having an open mind to continuous learning.
There are so many things we can learn, without having good grades or attending a school and still be intelligent.