Now, getting a facehugger on a Dragon, that would be interesting.
As for how the school would fare, not sure, three 11 year old children managed to defeat a Troll through panicky uncoordinated combat, and by the formation of the DA, students are less panicky in general (Heck, in book 7 it turns out Ginny is a beast in magic combat, it seems), so barring surprise attacks, the aliens might have a tough time. And given that this is a world were bones can be rebuilt overnight, I'm not entirely sure a chestburster would be fatal if the victim can be taken to the infirmary on time.
And what's this nonsense of Hagrid keeping a drone for himself? He'd keep the Queen!
