So you're going to charge teenagers with crimes based on "what they might have done" now? A bit minority report, don't ya think? This statement standing alone is a huge concern for civil liberties. Arresting someone and charging them for one crime based on your opinion of "what they might have done" seems remarkably heavy handed.
But who knows what this kid is like, perhaps he was a little hellion making this teacher's life a nightmare [was the teacher gay? homophobic? I don't know the back story here] and this was just the straw that broke the camels back? Eventually we all snap when pushed and kids know how to push your buttons better than anyone. Perhaps he needed be kept in check and have his boundaries enforced to reset his notion of what is and isn't acceptable conduct. But equally... a felony for a [hopefully harmless] prank that is common practice in I.T. environments around the world, that's a bit weak.
At least he's only a kid and it'll be sealed on his 18th birthday. However, it'll be attached to his school record and follow him around like a bad smell until he leaves academia. So I guess he'll learn his lesson... all be it a bitter consequence to what amounted to something largely harmless.