@Riger : Umm, what 'elite' class are you shitting on about?
He's in the same classes as the 3 kids, all the promotion exam does is letting him skip grades to study more advanced materials.
Which, if you think about how early exam are common enough to have precedents for it, then it's not seen as something that special.
He only took two exams so far btw, he hasn't skipped all the years yet.
And we don't know if the principal doesn't know about him, all we know is that the principal is busy so the teacher is telling Arel not to bother him (and he only was going to do so to take the exam)
As for him being in every class but isn't being noticed, the story established the reason already:
https://mangadex.org/chapter/933151/2
Heck, the only people who's aware he' in all 6 academies are the 3 kids with him.