Goofs

When Mike and Ned are sitting in the kitchen, icing their injuries after beating each other up, Mike's wedding band switches hands several times.

In the scene where Mike and Ned go to the principal's office to enroll in school, the principal's computer monitor switches from Dashboard widgets to the Flurry screen saver and back again.

When Ned calls off the Hummer it is immediately in the street behind the Principal, but was completely absent in every shot before that as can be seen by the street behind her being clear.

When Mark/Mike is comforting Maggie after Stan just broke up with her, the camera angle constantly switches in order for their faces to each be seen. When the camera is focused on Mike, Maggie's shirt is off of her shoulder, revealing her bra strap. When the camera is aimed toward Maggie's face her shirt is covering both of her shoulders.

When 17 year old Mike and Alex are walking towards the table in the cafeteria, Mike has his glasses hanging from the top of his shirt, but when he sits down it has gone.

At the game in the end the whole family is there. The daughter/sister then says "I thought Alex was interested in me, not you" to her mother. Alex is in fact the brother/son and the right name would have been Mark (since this is not GoT).

When back in 1989, Ned runs in late for the team picture wearing wizard robes and referencing a hippogriff, it may appear to be nod to Harry Potter (which was not published until 1997, and 1998 in America). However, the myth of hippogriffs is not a Harry Potter original, having been around for hundreds of years. Ned also makes reference to being "Dungeon Master", making it obvious he was playing Dungeons and Dragons, which has been around since the 1970s (hippogriffs included).

In 1989, Scarlett is pregnant with Maggie, yet in the present-day scenes Maggie is only 17. Although the movie was released in 2009, if you pay attention in the scene where the students are sending the video of the fight to each other, one of the cell phones clearly shows a date of 2007 for the movie setting.

In the scene on the morning after the big party, Ned and Mark (Mike) have a conversation and Mark (Mike) is wearing a red plaid shirt. In the very next scene, Mark (Mike) is wearing a blue shirt with a white undershirt. However, Mike tells Ned he needs his pants. If Ned had time to put his clothes on, Mike had time to change the shirt.

In the scene where Mike assists his wife with the shopping from the back of the car he runs his finger down the side doors. Two more finger lines are noticeable, suggesting previous takes.

At the big game in 1989, Mike throws a basketball over his shoulder (as he walks off the court to go after Scarlett). The camera pans down to show it bouncing vertically on the spot, but a real ball would be bouncing further and further away.

In 1989, a shot of the crowd shows a student in the front row wearing a pink and purple band t-shirt by the 21st-century band Paramore.

When 17 year old Mike is dancing with the cheerleaders in 1989, the coach calls him Vanilla Ice, who didn't make it big until 1990-1991.

There is sound effect of the ball being dribbled when in fact Mike is only holding the ball deciding who to pass to. It was not, as previously assumed, a double dribble, but the wrong sound effect.

Ned and Principal Masterson bond over "Lord of the Rings" trivia and speak a language they call "Elf." The correct name is "Elvish."

If this movie took place in 1989 in the beginning and 2007 for the rest. If Mike was 17 in 1989 and 37 in 2007. That would mean Mike was born in 1972. Meaning that the adult Mike would be 35 in 2007 not 37. He wouldn't be 37 until 2009. When the movie was released.