When the Lisbon sisters and the boys are playing music to each other over the phone, the song chosen by the girls starts playing while the head shell/needle on their turntable is descending, before it makes contact with the record.
When Trip is introducing himself to the movie, he talks about the first time he met Lux. He says he met her for the first time when he walked into the wrong history class. But when they show him walking into class, the door says Language Arts.
When Trip is pinning the flowers on Lux's dress, the camera pans down to her hips and a round 'inset' window appears, revealing that Lux is wearing pink panties under her dress, with Trip's name scrawled on them. The brief shot also shows part of her bare thighs and tummy. Yet when Lux is making out on the grass with Trip, we can see she's wearing white pantyhose (or tights) under her dress.
To show the Lisbon house's gradual dilapidation, the 7 on the house number above the door is sideways as if it was missing a nail. In a later shot that is meant to demonstrate the passage of time, the 7 is upright again.
When the boys are in Economics class they look outside, where they see Lux sitting on the grass. The guy that is with Lux throws some grass at her, but in the next shot the grass can be seen on her shoulder, but the guy didn't throw it there.
When the girls are locked up in their house, the front lawn is slowly covered with brown leaves to show the passing of several weeks. However, there is only one tree on the front lawn, and its leaves are green. The surrounding trees are also green and none of them show evidence of falling leaves.
The woman news reporter who comes to interview the family after Cecilia's death tells Mrs. Lisbon she's from Channel 2, when in fact we can clearly see from her news report moments later a Channel 8 logo on the screen (and on her truck).
When the boys are talking about traveling with the girls to the Far East, the narrator says that Cecilia hasn't died but is instead now a bride in Calcutta. However, the picture shown of Cecilia in traditional Indian wedding attire is in front of the Taj Mahal, which is located in Agra. Calcutta is in Eastern India, and Agra is in northern India.