Goofs

When Owen and Roddy are jokingly giving Duncan a hard time for flirting with Susanna, a girl wearing a purple bikini walks past them three times, going in the same direction each time.

In the first scene at the water park, Owen is eating a pop-tart. Throughout the scene, the amount of pop-tart eaten and the direction it is facing in his hand changes several times.

When Duncan meets Owen, Owen is in the middle of a game of Pac-Man on Level 1. He says he's never made it to Level 2. When we see the screen a number of dots and one of the power-pellets are missing. When Duncan loses Owen's last life, still on Level 1, the screen shows an earlier point in the game.

Susanna follows Duncan on her bike to the water park, yet on returning home she comes back with Duncan just with his bike.

When Owen talks about entering Duncan's name on the leaderboard, Duncan mentions you can only enter three letters of a name per score. In reality, Pac-Man doesn't let you enter a name on a leaderboard, only saving the high score with no leaderboard either.

Pam (Toni Collette) talks about how she met Trent (Steve Carell) at a Halloween party, then further says it was "almost a year ago" when the story takes place at the beginning of summer.

Duncan gets a job at 14 with no parent signing off on his employment, further seen he isn't even paid "under the table" when he receives a paycheck.

Close to the end of the movie, Trent pulled the station wagon into a gas station. The sign shows a gas price of $3.42 9/10 per gallon. That's the price of the 2010s and definitely not the 1980s when the story was supposed to happen.

When Susannah (AnnaSophia Robb) closes the tailgate to the station wagon after Duncan (Liam James) climbs in, she lifts up from the bottom to close the tailgate. A few minutes later when Duncan jumps out at the gas station the door opens sideways like a passenger side door of a car.

A feature of this model station wagon was the dual acting flip/swing tailgate, where it could be opened like a car door or like the tailgate of a pickup truck.

Near the end, when they stop to fuel up, many think that because the pump handle is green that it is diesel being put into the station wagon. While many diesel pumps do have green handles, that doesn't mean all green handles are diesel. The pump he is at has octane ratings and a sign stating that it may contain 10% ethanol, proving that it is just gasoline.

The father character questions Duncan on whether he knows how a dent occurred on the roof of the car. Duncan was shown leaping off of the vinyl-covered roof and no damage was evident.

Microphone visible inside Owen's shirt when he and Duncan are on top of slide.