In Entertainment Weekly, Emma Watson reported that she took the role because director/writer/novelist Stephen Chbosky told her that "Not only is this going to be one of the most important parts you play, you're also going to have the summer of your life and meet some of your best friends." She also reported that the claim came true.
According to an interview with Writer/Director/Novelist Stephen Chbosky, "watching people like Emma Watson, Logan Lerman, Ezra Miller, and Mae Whitman who never had prom, never really had a proper graduation, because they were always working, and watching those kids get to have a high school experience that we all take for granted was very special."
The novel, "Perks of Being a Wallflower" was first published in 1999, but the action is set during the 1991-1992 school year. No explicit year is mentioned in the film, though based on several plot details (i.e. no characters use cell phones or the Internet, the use of records and cassette tapes) and the inclusion of the song "Low" by Cracker on the soundtrack (released in 1993), the movie does imply a mid 1990's setting.
John Hughes originally bought the film rights with the intention to write and direct. He intended to make the film as more of a dark comedy with Shia LaBeouf set to play Charlie, Kirsten Dunst slated to play Sam and Patrick Fugit cast as Patrick. Hughes sudden death stalled the project, as he'd not completed a script before his passing. This allowed the film to be revived as an independent movie with novelist Stephen Chbosky returning to script & direct.
In an interview with LAYouth.com, author Stephen Chbosky said that he wrote the book for personal reasons, but realized that many people related to it while reading the book's customer reviews on Amazon.com.
At the time of filming Ezra Miller was 17-years old, about the same age as his character. Logan Lerman was 18-years old, two years older than his character, who turned 16 the day before Christmas, and was an old freshman after being held back a year. In reality, Lerman is 9 months older than Miller who plays a character close to four years his senior. Emma Watson was 21-years old at the time of filming making her the oldest of the three main actors.
In an interview with Movieline, Ezra Miller said that he first saw The Rocky Horror Picture Show (1975) when his older sister showed it to him as a young kid. At the end of the movie, his sister turned the TV off and said, 'you can't tell mom and dad'.
When the family is eating dinner at the end of the movie Charlie asks his dad how he thinks the Penguins will do this year. The Dad replies that they will suck and need to learn defense. The Penguins went on to win their first Stanley Cup that year.
Was originally rated R by the MPAA for "teen drug and alcohol use, and some sexual references" but was later changed to PG-13 after an appeal for "mature thematic material, drug and alcohol use, sexual content including references, and a fight - all involving teens"
The picture inside Charlie's school locker (when he wears his Christmas suit to school) is the singer Johnnie Ray. At the school dance when Sam & Patrick perform "the living room routine" to Dexys Midnight Runners's Come on, Eileen, the first line of the song is: "Poor ol' Johnny Ray..."
Writer/Director/Novelist Stephen Chbosky, is a native of Pittsburgh where the movie is filmed and set. In an interview with Hollywood.com, he reported that his parents have breakfast 3 times a week at one of the filming locations, King's Restaurant.
Though it isn't mentioned in the movie specifically, Charlie is not that far apart in age to Sam and Patrick, perhaps one of the reasons he connected with them so well. If you pause the film, you can count 16 candles on Charlie's birthday cake, which he receives on December 24th. A December birthday would make him an older freshman, but Charlie has also been held back a year due to emotional problems, which is mentioned in the book, but not the movie. Hence, when Charlie turned 16, most of his Senior friends were probably still just 17 years old, making them very close in age.