I have heard that a couple of famous geniuses, who are mostly likely typed as NT's did badly or average in school, but they only did badly because they were disinterested.
if you think about the abstract concept that is school, then the way you are judged in that concept is fundamentally different from the purpose. Being taught stuff is a good thing, a thing all NTs will like. Some topics are more boring than others but thats ok for most NTs, they will go on even with a boring topic having the convenvience that it plays a greater significance in something. But then comes the way you are judged for things: 90% of my university lectures were based on rote learning. You got a 180 pages long transcript for the lecture had about 6 semester time to eat it and then spit it all out in one final exam. if you do well in that, you are officially declared as "intelligent". On the other hand, the other 10% like mechanics, math, thermodynamics, were the most hardest lessons of them all and most people drop out of University because of them.
The greatest difficult for me in school was that it followed a bottom-up strategy. I was never intrested in stuff, cause I didnt know what it was good for.
So tho my greatest intrest was natural science, I majored in english and german literature studies, cause that was more fun than doing derivations I have no clue what they are good for. Then at University I gave natural science another try and was first of all taught the big picture, so it followed a Top-Down strategy. And that was intresting cause finally I saw what cool gadgets you can build by having the mathematical solution to a differential movement equation of the first order.
I am good at math, but I suck at rote learning; does that mean I am more intelligent ? No it doesnt, basically it is a talent or a preference and thats it. Those people who are labeled as intelligent in society have mastered to, despite their talent or non-talent, excel in every topic and achieve an overall good GPA. That is indeed an achievement, if they should be called intelligent, I dunno; I'ld rather go with hard workers.
I am not very intelligent, I have a talent for certain things but thats basically it. I am good at understanding complex systems and deriving possible future developments in those systems. I am good at understanding boolean logic, computers, electronics but quantum physics is a bitch to me. I am good at the abstract perception of the concrete but I suck at making something abstract up from nothing or little facts (a Ni quality imo) like quantum physics.
Given all that single thoughts, to me it is a no-go to label people as only intelligent or not. This like saying music is only good or bad, when there is so much more to it. if you asked me if I would have wanted to have only good grades and be labeled as a genius ? Of course who wouldnt. But I wouldnt have wanted to pay the price for it. Since things do not come natural to most people, like they would come to a genius, most people have to invest a huge deal into their successful studies and to get a good GPA. I respect those people, it's their decision, but my decision was always to choose comfort. That way I had more time in my youth, to develop a personality and form a stable reliable character. So my choice was not pointless, I just choosed to concentrate on a different thing. Since that is very dangerous cause you actually harm yourself by acting against what society wants from you, I embarked on a dangerous path. Still I like danger and I like to go those paths least travelled, therefore I've made my choice.
Sometimes it's frustrating when you see what dumbasses get labeled a genius just because they scored high on a rote learning exam. Then again those people appear as dumbasses to me cause I have developed into a different direction, which doesnt place importance on achievement. In their circles achievement may be the only importance, therefore they appear to others who dont value that as dumbasses.
Its all always a matter of perception and it can drive you crazy if you think about all the options. But the only important thing is that you are always concious of your choice of option and that you stick with it and know why you have choosen it. If you run around all your life being envious of the great achievers, you'll miss becoming happy yourself in your life. That doesnt mean at some point that you should settle for less, but that if you want to be a great achiever yourself, you need to work on that.
I never considered the NT temperament to be expectionally genius, to me thats a false definition all along. The NT temperament isnt moved by tradition and prefers sometimes to be a loner, it isnt moved by the thrill of action and the adrenaline rush and it doesnt decide upon what feels best for them or whats best as in ethical in the great societal picture. No it has choosen to make decisions based on whats real and understanding whats real and graspable, its a way to rationally, empirically paired with a portion of what could-be'ly living your life. There is really no claim a NT could have to be labeled a genius or exceptionally intelligent. It is imo rather societies fault, if they put one of the 4 temperaments on such a high throne because it could be the one best-suited for their workforce. But thats another philosophical topic...