I do agree with the second part of the statement, I really want to avoid promoting alts as to not distract the students from the true store of value.
Since you're a math teacher: how about an exercise to calculate how much Bitcoin they would have had if they would have invested 25% of their entire allowance since the first time they got it?
That's probably also a good moment to emphasize that exponential growth in value will probably turn into an S-curve at some point.