After she had written the script, Sofia Coppola was heartbroken to discover that another company was already producing an adaptation of the book themselves. However, they were not happy with their script, so she showed them hers and they ended up using it instead.
At the beginning of the film the workers apply a "Notice for Removal" tag to a diseased tree. The tag reads "City of Gross Point Parks Department." This is a misspelling of the name of the city in which the book and movie take place, Grosse Pointe, Mi which is a bordering suburb of Detroit. Jeffery Eugenides, the author of the novel, was born in Detroit and attended University Liggett School in Grosse Pointe.
When the girls are on lock down you watch the days go by with a view of the house. This was after the tree in the front of house was supposedly cut down, yet the tree is visible in the whole season montage
In the Danish version of the dvd, you can't figure out the age-order of the sisters. It said that Therese and Lux was twins, while in the movie Therese is the oldest (17 years old) while Lux is the 2nd youngest (14 years old). In Real life Bonnie is the 2nd youngest of the 4 actresses (Therese, Mary, Bonnie and Lux) , while Therese and Mary is both born in 1978.
The trivia item below may give away important plot points.
The pre-homecoming photo of the girls foreshadows their deaths. Lux is holding her hand out to feel a leak coming from above (her hand's position resembles holding a cigarette) - later when she dies, her hand is seen hanging out of the running car in the closed garage, holding a cigarette. Therese's eyes are closed, and she died from an over dosage of sleeping pills. Bonnie's arm appears to be scratching her upper back, but also resembles a hanging - which is how she died. And after the photo was taken, Mary coughs, and she died from sticking her head in the oven.