The Motion Picture Association of America (MPAA) defines the R rating as, "An R-rated motion picture, in the view of the Rating Board, contains some adult material. An R-rated motion picture may include adult themes, adult activity, hard language, intense or persistent violence, sexually-oriented nudity, drug abuse or other elements, so that parents are counseled to take this rating very seriously. Children under 17 are not allowed to attend R-rated motion pictures unaccompanied by a parent or adult guardian. Parents are strongly urged to find out more about R-rated motion pictures in determining their suitability for their children." (http://www.mpaa.org/ratings/what-each-rating-means).

It can certainly be argued that the mental image of reading such material is at least as strong as the visual image in a movie. If a parent is "strongly urged to find out more" about a movie with these types of themes, then s/he should also be strongly urged to find out more about these themes in required reading lists defined by schools. This amendment is not banning any books, as some commentors seem to suggest, but about notifying parents about sensitive material in required reading.