Mockingbirds label as a classic?

This novel is clearly a classic and has been acknowledged by several sources as such. Harper Lee was awarded a Pulitzer prize for the text, and Wikipedia lists several pieces of data which indicate the book's popularity, longevityand social significance.

...'it has sold over 30 million copies and been translated into over 40 languages.[86] To Kill a Mockingbird has never been out of print in hardcover or paperback and has become part of the standard literature curriculum. A 2008 survey of secondary books read by students between grades 9–12 in the U.S. indicates the novel is the most widely read book in these grades. A 1991 survey by the Book of the Month Club and the Library of Congress Center for the Book found that To Kill a Mockingbird was rated behind only the Bible in books that are "most often cited as making a difference".'

Apart from its international popularity and validity, as a teacher of 18 years and a lover of great literature, it is in my top 10. The characterisation of a woman reflecting on the turning points of her childhood in the climate of seething social injustice is at once compelling, humorous, tragic and optimistic. It is a timeless portrayal of a time we should not forget.