Some classmates might be understanding. They could have been taught to be inclusive and kind, so they don't make a big fuss. However, there are also likely to be some classmates who are curious or even a bit mean. They might tease the child, not fully understanding the situation.
One common theme is his growth as a sorcerer. Many fanfics focus on how he hones his skills and becomes stronger. Another theme is his relationships, like his friendship with Yuji or his complex connection with the Zenin family.
His classmates would probably be very concerned. Some might immediately run to get the teacher or the school nurse. Others might gather around Peter, asking if he was okay and trying to comfort him.
There's a fanfic called 'Megumi Fushiguro: A Different Path'. In this, the author takes Megumi on a completely different adventure from the original story line. It's really interesting to see how his character develops in this new scenario. Also, 'Megumi's Hidden Powers' is a fanfic that uncovers some potential powers that Megumi could have, which makes for an exciting read.
Captain America would probably be very reflective. He might see his past self as a reminder of his long journey and how much he has changed. He could try to offer some words of wisdom to his younger self.
Well, some past gods might be amused. They'd see these modern interpretations of their stories and characters in the Percy Jackson fanfiction as a strange yet interesting new form of worship or at least attention. For example, Zeus might be a bit irked at some of the liberties taken with his character, but also secretly flattered that people are still so interested in him.
Well, Boruto could be very inspired. Naruto's past is full of struggles, from not having parents around to being constantly underestimated. When Boruto discovers this in the fanfiction, he might realize that his own problems are not as big as he thought. He could be motivated to work harder and not take for granted the things he has, seeing how much Naruto had to fight for everything.
Some gods might be entertained. For instance, Hermes, being the trickster god, might enjoy seeing the different and often humorous takes on the gods in the fanfiction.