(I would prefer for the teacher to be female, but a male teacher makes more sense in this setting since most of the teachers in the fire nation schools are male; this is why I put either gender, to further advance Avatar's all-inclusive message; all I ask is that these lines be delivered with their original intent; when the teacher hears one of the students mentioning that the boy that they took in is the Avatar, he or she is very shocked, as this person had been consorting with some nobles earlier and they were all convinced) So, is it true that you're the-? 

(the teacher hugs Aang supportively once he or she hears that Aang is the Avatar; but the teacher is doing nothing more than being supportive) I can't imagine the burden of responsibility, you must be carrying now, young boy. (sighs) For such a burden to be placed on a child...the spirits can indeed be cruel. 

(shakes his or her head) I would not dream of trying to stop you, Aang. Just do your  teacher and classmates a favor and do your best to survive the fight with the Firelord, okay? (a bit of sympathy in this last bit) I cannot imagine what it's like to be the last of your kind. If you ever need anything from me, don't hesitate to look me up. I live here in the capital, surrounded by cats. I find stray ones lying around all the time and can't help myself but take them in. Thank goodness my house is on the outskirts and very large! Otherwise, I might not have room for them all. I will see you around. Good luck!