I don't have any classes to use with pen pals at the moment, but I do have a suggestion:
There is a website called Postcrossing (click word for link) that you can use for free. Basically, members around the world are chosen at random to send you postcards, and you/your class will send random people postcards in return. And, you can arrange "Direct swaps". Using a postcard is a little less intimidating than a 8.5"x11" blank piece of paper.