Mae Whitman stated that she was frequently bullied in high school growing up and ate lunch in the bathroom on occasion to avoid bullies. These experiences helped her get in the mindset to play her character in the movie.
Though the source book, The Duff by Kody Keplinger, and movie share the name, the plots are completely different.
Bella Thorne's character, Madison, is written specifically for the movie. She did not exist anywhere in the book.
The girl Wesley (Robbie Amell) makes out with in his intro is his real-life girlfriend (and as of 2016 wife) Italia Ricci.
Filmed with an R rating in mind. It was then decided during post-production to make it more "family friendly" and it was edited to obtain a PG-13.