A tumblr dedicated to Avatar Aang: a kid who lost his entire race, saved the world and managed to get a girlfriend -- all in one year.
Avatar: The Last Airbender and The Legend of Korra blogged about here.
Tenzin knows more than he is letting on. My guess would be that Aang told the rest of the world that only the Avatar had the ability to take bending away. But his close family and friends know it’s a technique that can be acquired by a special few.