Well, this looks interesting...

The relationship between them is really cute and adorable...

Surely the best punition you can imagine

Gotta admit, I'm freakin' annoyed with Vapor so far. ^^; They're young, horny teens, okay, fine. But they got the once-in-a-lifetime chance of training to become a wonderbolt, one of the most prestigious ranks in pegasus society. And they fucked it up. Not once, not twice, but thrice. They apparently should've been kicked out after the first or second incident, but Spitfire, despite her harsh demeanour, was nice to them. And even after they fucked up a freakin' third time, Spitfire still tries to give them a chance. Yes, this is meant to be punishment. They aren't supposed to come out of this thinking 'yay, that was great, let's do it again!', obviously. It's a weird punishment, for sure. But Vapor huffing about it? Feeling/expressing disdain towards Spitfire? Get your head out of the clouds, filly, this captain of yours has been nothing but forthcoming! Even now - after you fucked up thrice and are given yet another chance - you could just, oh, you know... bear the consequences of your own inadequate self-control and leave. You could just not take the punishment, not take the fourth chance and do something else with your life. Being a wonderbolt is about discipline. The thing Vapor - and Sky - seemingly just don't have.
To be blunt... they're, as of right now, ungrateful pricks.
Makes it hard to sympathize with them.

On the other hand, though: Spitfire, the hell were you thinking? 'They can't stop fucking, literally, so let's make them fuck in a supposedly uncomfortable setting, that'll teach 'em!' There's sooo much wrong with that train of thought. First and foremost, though: It won't work. Having sex is kind of a demanding process, you know? Their focus - probably - will be on their partner. (Eventually. If they even manage to 'perform' at all.) So the 'uncomfortable and thereby teaching setting' will lose quite a lot of weight once they actually get started and get into it. Adding to that, it probably won't discourage them. They're horny teens. Indulging their instincts doesn't 'exhaust' them, that's not how it works. Teach them discipline of kick 'em out! Oh and what about the other cadets? You know, the other probably horny, barely self-controlled colts and fillies? With that kind of spectacle ingrained in their memories, I'm sure they'll find it much more easy to concentrate than before, right? ... right...?

In conclusion: Spitfire is trying her best, but as seen in the show - continuity! -, she's awful at picking the right tool/path for the job. And Sky and Vapor deserve to be kicked out.

Well, that went into quite a tangent. Gonna read the rest now. (I have a feeling I'm overanalyzing things... hmmm... I wonder where that comes from...)