When Scott Voss is riding his motorcycle to the school, he is wearing boots. When he opens the window and enters the classroom he is wearing sneakers.
When eating with Niko, Marty, and Mark the night before a fight, Scott Voss gets pied in the face with a cherry pie. The remnants of the pie are shown in one shot under his nose, then it flips to another shot and is under his nose and on his chin, then flips back and is only under his nose again.
When Scott Voss is at the vending machine, he pulls out two packets of chips that drop, throwing one to a student who saw him. In the next shot he is seen holding two packets of chips again.
During the final fight scene with Ken Dietrick the end of Round two is crowned by Dietrick throwing a Haymaker into Scott's lower jaw. This knocks out Scott's mouth guard, you see the mouth guard fly out of his mouth, and land on the wire of the octagon, in the next shot you see it still hanging on the wire. Yet Scott has to hazily walk halfway across the octagon to retrieve his mouth guard from the floor.
When Kevin James is riding his motorcycle to the school, he is wearing boots. When he opens the window and enters the classroom he is wearing sneakers.
At about 20 minutes into the movie, Niko runs out to Scott to ask for help in passing the citizenship test, claiming that if he fails, he will "be sent back to Holland". If Niko is eligible for citizenship, this would mean he is already a Lawful Permanent Resident, and therefore would not be sent back.
When it starts to rain, during the second fight, this would have stopped the fight immediately, as not only is there a risk of serious injury but if it thunder or lightning would strike, it could potentially harm the fighters. Clearly done for comic effect, and not realistic at all.
Leaving the Oath Ceremony, none of the new US Citizens are carrying a Naturalization Certificate.
When Mr. Voss is riding his motorcycle across the football field at the beginning of the movie there's a maintenance guy lining the field with a chalk lining machine on an obviously artificial field with painted lines.
With the amount of money Joe Rogan spent to bring the school orchestra to Vegas, he could have just instead saved the music program.
Just prior to Niko approaching Scott to ask for extra help, Scott looks at his check for teaching the citizenship class. In the upper left corner, it appears the check is from the "INS". The INS has not existed since 2003 (nor does it offer citizenship classes).
When Scott, Marty and Niko are coming out at the third fight, there is clearly a camera crew guiding them to the ring.
The calendar on the desk of Vice Principal Elkins's reads January 2012. However, about three days later, when Malia show Scott the YouTube video of Scott vomiting on "Lucky" Patrick Murray, the video's description displays an upload date of April 2011.
Elkins tells Voss that he played the French horn in marching band. The French horn is not a marching instrument. Horn players usually play the mellophone when marching.
After sparring at the Sityodtong Gym, when the guys sit down for pasta with meatballs, Mark DellaGrotte quotes scripture, stating it's Genesis 32:24, but the scripture he quotes is actually Genesis 32:25 (KJV)