My school never had a pen pal assignment. When I was 12, a magazine I used to read called Teen Magazine
ran a "Meet Your Astrological Pen Pal" piece. You had to tape 50 cents to a form and check off the attributes you wanted in a friend. I got the name of a girl named Johanna, who lived in Newark, NJ. We corresponded for a bit, but she kind of fell of the face of the earth. I was really disappointed. Shortly after, I received a letter for a girl from Redgranite, WI. I guess they sent me Johanna's name and address, and sent mine to the girl in WI. We became fast friends. We corresponded from 1981 until 1987, when I flew out to meet her. Then we met again when I was the maid-of-honor at her wedding in 1991. In 1998 she came to NYC when she was in my wedding.
We no longer write to each other, but keep in touch through FB and send each other cards at Christmas/birthdays.
I wouldn't feel comfortable with someone in prison having my name and home address.