Okay, I know that Tails is a boy (I've known him for a quite long time) but I heard he was girl. Was he a girl at one time in his life, or was he always a boy?
Originally Tails was a girl, this has overall been proven and accepted fact by most people. What changed however was when Sonic 2 was being produced Sega of America basically said that the game needed to have a male Tails because of ethics back then and they did not want a female girl running after Sonic. So Tails was made a guy and later on they introduced Amy to run after Sonic.

~Ron Prower (yeah I finally decided to do one XD)