Amnesia in the classrooom?

[Kman]

Ooooh... This is kind of tough simply for the fact that there aren't very many serious stories that create atmosphere but get to the scares quickly too. I think your best bet though would be Black Forest Castle or An Unexpected Arrival (though An Unexpected Arrival does have ONE jumpscare, it is also VERY atmospheric and it's pretty good), you could also try Nepsis or Followed By Death (though you might want to run through these two ahead of time since they take a little longer to get going on the scares). Another possibility is the Justine DLC, since it gets to the scares pretty fast too (but again, you'd probably have to run through it first to make sure you could actually get to the really good parts in 20 minutes).

On a side note, your psychology teacher sounds like a total badass. Seriously.