(L to R) Logan Lerman, Ezra Miller and Emma Watson star in “The Perks Of Being a Wallflower.” (John Bramley)

Stephen Chbosky’s 1999 young adult novel “The Perks of Being a Wallflower” could be a memo about the importance of inclusiveness. The book’s protagonist, high-school freshman Charlie, is rescued from bleak loneliness by a circle of friendly misfits who embrace him, shyness and all. And just like that, a sweet-natured kid transforms from outcast to cohort.

So maybe it follows that, when adapting the story for the big screen, Chbosky vowed to reach as many people as possible — and not simply for the typical reasons of tallying box office numbers and dollar signs. Teenagers had written letters to Chbosky over the years after they had found something like salvation in the pages of his book, and he hoped for the same result with the cinematic story of Charlie, played by Logan Lerman, and his new friends Sam (Emma Watson) and Patrick (Ezra Miller).

Just one thing stood in the way of the filmmaker’s sweeping endeavor: The dreaded R rating.

“A 13-year-old kid can get my book pretty much anywhere. [They can get it] from the library; they don’t have to get permission to buy it from a bookstore. For all the reasons the book has done good for those kids, I wanted them to have the same access to the movie,” Chbosky said recently while in town from Los Angeles. “So I was deliberate from Day One: Okay, where is the line, and how can I push it?”

While the MPAA initially stamped “Perks” with an R, an appeal ruled in the writer-director’s favor for a PG-13 designation. Reaching that ultimate goal wasn’t an exact science, but there was one fairly ironclad dictum, Chbosky found. You can only use a certain word — the mother of all curse words — one time.

Logan Lerman stars in “The Perks of Being a Wallflower.” (John Bramley)

“There was a contest, because no kid knew who was getting the” word, Chbosky said. A few scripted instances fell flat. But in a moment of inspired improvisation, Miller, observing an ill-advised romantic overture, remarked in a deadpan: “That’s so [messed] up.”

“And it was so funny that I was like, I gotta use that one,” Chbosky said. “And so Ezra was very proud and very gloaty.”

Bad language is not the film’s only transgression. Plot points, including underage drinking, suicide, drug use and sex, have landed the work on many banned book lists. But, given that the story is semi-autobiographical, Chbosky finds the controversy a little insincere.

“A lot of these things that are going on are in middle schools, and we all know it,” he said.

“Perks” is Chbosky’s most personal work — his self-proclaimed baby — which is partly why he took his time adapting it. In the intervening years he gained experience with screenwriting, working on the television series “Jericho,” as well as the screenplay for “Rent.” But there were mental and emotional reasons for the wait, as well.

“I needed the distance from it, but not so much distance that I forgot what it was like to be a kid,” Chbosky, now 42, said. “My secret hope is that it will be as exciting to a 15-year-old in high school as it will be to their 50-year-old mom or dad.”

It’s a tall order, but the film has a way of reminding viewers — even those with childhood far in the rearview mirror — about the stress of navigating high school and how all-important it can seem to find a place to belong. Always the observer, Charlie takes note of the jocks and the hippie-ish environmental club; he weathers the taunts of bullies and thankfully ends up with a standing date, singing along to “Rocky Horror Picture Show” with his new friend-family. But even after that, a sense of melancholy persists amid the heightened emotionality of high school, a time when every little thing feels amplified. The loneliness, in the book as well as onscreen, remains palpable.

While high school movies generally fall into the genre of crude comedy — think “Superbad” or “American Pie” — growing up isn’t all child’s play. “Heartbreak is a rite of passage for adolescents,” Watson noted in a recent interview.

Chbosky spent long hours tapping into that well when he worked on the book, and yet the movie version felt like a more personal process, he said. Filming meant coming home, shooting in Pittsburgh and the suburb where he grew up, Upper St. Clair. But new obstacles lurked under all that familiarity.

“When I started, because I was a first-time studio director and I knew that there could be challenges or scrutiny, I was much tighter at the beginning,” he said. “I was very fiercely protective, and then over time I realized everyone’s just trying to help make a great movie. That’s all anyone cared about.”

In a way, the advocate of inclusiveness had to remind himself of the importance of open arms while on the job, especially when everyone is headed toward a shared goal.

“What I learned is how much people have in common and how people share the same fears and the same passions and the same desires to be free of whatever it is that’s binding them,” Chbosky said. “It’s a much bigger tent than you think it is.”

“The Perks of Being a Wallflower”

Opens Friday in area theaters.