Schools and children across America may struggle to obtain a copy of "To Kill a Mockingbird" after April 25. The novel's author Harper Lee's estate will no longer allow the publication of the mass-market edition of the American classic.

Hachette Book Group, which publishes the cheapest version of the book, announced the discontinuation in an email to booksellers on March 4. No other publisher will be able to produce a mass-market edition either.

The email and an attached PDF suggested different accounts on who made the decision to end the mass-market edition. The email stated it was "per the author's wishes" while the PDF read, "as per the wishes of the author's estate."

The stoppage of this edition will most affect schools across the country. Since its publication in 1960, nearly three-fourths of schools have taught "To Kill a Mockingbird." Only "Romeo and Juliet," "Macbeth" and "The Adventures of Huckleberry Finn" have been assigned more by English teachers.

The mass-market edition retails for $8.99 and most schools would get a bulk deal for 50 percent off, paying less than $4.50 per copy. HarperCollins will continue to publish a trade paperback version, which will sell between $14.99 and $16.99. The publisher will also print a hardcover edition, special editions and digital copies (i.e. Kindle).

HarperCollins also published the "To Kill a Mockingbird" prequel, "Go Set a Watchman," last year. Lee, who died on Feb. 19, wrote the book in the mid-1950s, but put it aside to write the book that would go on to win the Pulitzer Prize.

Tonja Carter, Lee's lawyer and the executor of her estate, discovered the "Go Set a Watchman" manuscript, but some have questioned if Lee ever wanted the story published. A statement released at the time of the new book's announcement included quotes reportedly from the author.

A week before her death, Hollywood producer Scott Rudin obtained the rights to adapt "To Kill a Mockingbird" into a Broadway play. Rudin will produce and Aaron Sorkin will write the script for the play, which will premiere during the 2017-2018 season. The movie adaptation of the book, starring Gregory Peck, won the Oscar for Best Picture in 1962.

Mass-market editions have declined over the years. Classic novels such as "The Great Gatsby" and "The Grapes of Wrath" have discontinued the practice.