I recently rejoined a type of mentoring/pen pal program called In2Books. It connects elementary school children with adults through reading and commenting on the same books.
During the school year, students select 5 books from lists compiled by children's literature experts and exchange online letters about the important issues in the books.
I have participated in the program twice and the organizers continue to improve the quality of the software used for the exchange of letters. Initially the 5 books to be read were free and were sent to the adult's home. Now the adults must buy the books or get them from the library, but I consider this a worthwhile investment.
The program always looking to sign up for new members. I like several aspects of the program. One is that there is a background check on the adults who participate and another is that they provide a lot of guidance in the writing of the letters.