When you read the book you see what a missed opportunity this film was
I actually saw the film first and I really liked it. I ended up actually ordering the book written by Emily M. Danforth and was shocked with how much the film version leaves a good chunk of the story out. I give you a synopsis of what was left out
"The Miseducation of Cameron Post begins in the summer of 1989 in Miles City, Montana, when protagonist and narrator Cameron Post is 12 years old. Cameron has been shoplifting and kissing her friend Irene Klauson while her parents die in a car accident at Quake Lake, which they visited every year. Cameron's very religious Aunt Ruth moves in with Cameron and her grandmother. Cameron begins renting VHS movies and decorating her old dollhouse to cope with her grief, and stops spending time with Irene. Irene's family discovers a fossil on their property, which results in great success and wealth for them, and Irene goes away to a boarding school. At Aunt Ruth's request, Cameron begins attending a new church, Gates of Praise, and its youth group, Firepower.
During the summer before starting high school, Cameron becomes close friends with Lindsey Lloyd, who joins the swim team with her while she stays with her father in Miles City for the summer. Lindsey is a lesbian and tells Cameron about her experiences with gay pride in Seattle, where she lives during the rest of the year with her mother. Cameron and Lindsey pursue a casual relationship, which mostly consists of kissing. They stay in touch after Lindsey returns to Seattle at the end of the summer. Aunt Ruth begins dating Ray, who sells frozen goods around the local area
Cameron becomes friends with Coley Taylor, who is in her biology class and starts driving her to Firepower meetings. Cameron develops a crush on Coley, despite the fact that Coley has a boyfriend, Brett. Coley convinces Cameron to join her and Brett at prom. Cameron invites her best friend Jamie to prom. On prom night, Jamie realizes that Cameron is attracted to Coley. He thinks Cameron is confused and kisses her. Cameron and Jamie begin dating after that, but Cameron is never interested in anything beyond kissing him.
Cameron and Jamie argue and break up at Miles City's annual Bucking House Sale because Jamie hooked up with another girl. Cameron goes home with Coley and they kiss, leading Coley to feel very confused. Over the following summer, Cameron and Coley both get summer jobs and Brett goes away for soccer camp. Cameron and Coley begin going to the movies after work to kiss in the dark. Meanwhile, Ruth and Ray get engaged. Cameron learns that one of the lifeguards with whom she works has dated a girl before. Reverend Rick Roneous, the leader of a new full-time school that treats gay people called God's Promise, visits a Firepower meeting, which makes Cameron and Coley uncomfortable.
Coley gets her own apartment in Miles City. Cameron brings a movie to watch with Coley alone in her apartment, which features lesbian vampires. Cameron and Coley drink alcohol and begin kissing during the movie, then have sex in Coley's bed. Coley's brother Ty and his friends interrupt them and Cameron quickly leaves. Cameron feels upset after work that day when Coley doesn't visit her and decides to make out with her coworker. When Cameron returns home, she learns that Ruth invited the pastor to the house and announces that Coley revealed what they had done together and as a result sends Cameron to God's Promise."
I know you can't fit in everything to a film but they could have added another 45 minutes onto the film with a lot of that stuff and actually made a better film imo. God Promise stuff takes up 30% of the book. The film is still very good and performances are all great but it does feel like it would have been better suited for a 8 part mini series on a streaming site. You could honestly do one now and it would feel totally different to the film version.