British vs. American English

There are many differences between British English and American English. Of course pronunciation of words like "tomato" (American -long a) and "tomato (British - short a..kind of stretched out for effect like bowing to the queen) and the spelling of American "color" and British "colour" are well documented differences. But the word that trips me up every day when showing students flash cards is the picture of an eraser. The students yell out RUBBER and I try really hard not to laugh. I really want to explain that it might not be a good idea to call an eraser a "rubber" if they plan on attending university in America. But where do I even begin...other than to say that "In America we call a "rubber" an "eraser?"