Learning Through Adoration

Question: Why does Instant Seminar only last for a scene? Teaching them a skill would probably be an entire scene by itself, and then when it comes time to use the skill they have lost the benefit.

Not at all! Instant Seminar isn't about teaching mortals a skill; it's about using your magical force of personality to will them into being better at it for a short period of time. It's actually pretty much the opposite of teaching people a skill, because they're not really learning it and are going to forget it as soon as you leave.

Instant Seminar doesn't require any kind of teaching montage to work (though, of course, you may stunt one if you like!); all it needs is a few words or sentences from the Scion to explain to mortals what he wants them to do. They're then so filled with inspiration that they go forth and do better at that skill in an attempt to please him, essentially motivated so strongly by his Charisma that they do better in spite of their normal limits. And while telling mortals to go do something is certainly part of a scene, it's definitely not the whole thing - they're free to go do their thing for the rest of the scene thereafter, until the Storyteller deems that it's time for them to move on.

If you actually wanted to teach mortals something, you'd need for them to genuinely learn it, which would probably involve Teaching Prodigy and that training montage we mentioned above. Depending on how you played it, that might take a scene, but Instant Seminar definitely doesn't. It's a knack that exists for Scions who want to inspire their targets to perform impressive feats for a little while, as opposed to actually teaching them anything they're going to retain later.