Iruka isn't an idiot. There's no way that kid is a demon. If he was, he would've razed the village to the ground by now. And if he's just possessed but can't use the demon's power, then he would've just run away or tried to break his seal. It's honestly baffling that so few people can make this connection.
So, clearly this is just a normal kid. That makes the teachers' attitude absolutely shameful.
So he's smart. That doesn't make him evil. That certainly doesn't justify scamming him out of test scores that he earned.
And so what if he's a prankster? So was Iruka. Of course, it was a pain to deal with the cleanup, but Iruka can certainly appreciate the artistry of a prank well done.
Naruto must be lonely. He needs more affection in his life. And as the only sane person in the whole village when it comes to this kid, Iruka will try his best to make sure that Naruto has at least some affection to fill the void.
"Hey Naruto! I'd like to talk to you about your last test. What do you say to some ramen while we talk?"
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-Naruto-
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Iruka-sensei is officially Naruto's favorite person ever. Naruto didn't know how he had never experienced this blissful heaven before, but he was never going to forget it. He'd gladly spend his whole monthly allowance here!
Iruka, on the other hand, was watching with morbid fascination as he watched Naruto practically inhaled his twelfth bowl. He was already regretting his life choices.
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-Kurama-
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This was actually disturbing. Kurama was convinced that the water in his sewer was literally turning into ramen broth. Oh, well. Might as well take advantage of this.
"You know, protein is essential for a growing boy. Eating a lot of it will help you grow up to be a really strong ninja. Perhaps if you love ramen so much, you should have chicken ramen to get more protein."
If Kurama was going to have to deal with all the ramen, maybe he'd get lucky and the kid would get some good meat too.