...Recently, he expressed his frustration about his teacher and classmates labeling bitcoin as a ponzi scheme or a scam each time he talks about it...
One of the characteristic features of the ponzi scheme is the promise of a guaranteed profit, which is absent when investing in bitcoin. Understanding such fundamentals can easily identify where the dangers lurk. But this is unlikely to help the teacher understand this, since he has already formed a negative image in relation to bitcoin.
Well I have no doubt about the teachers ignorance towards bitcoin. Maybe the teacher must have had experience with the Ponzi things hence their counter actions against your nephew and labeling bitcoin a Ponzi, but I was wondering if they do research in any way because it is only an updated teacher that could be able to absorb the knowledge of your nephew when explaining it to them. This should have been a research key or possibly an assignment they should have taken upon themselves to making sure they have knowledge about bitcoin so as to educate themselves more about bitcoin.
This display of ignorance by the teacher is something else if I were your brother I would do the needful because this shows how backwards they are possibly in academics and otherwise.