Continuity mistake: When Carter is splashed as the twins jump into the pool, only one side of his head/hair is wet. In the next shot, all of his hair is wet. (00:56:50)
Continuity mistake: When David and Ryan force Austin to participate in the bachelorette 'Dating Game', the CD player sits on the bench beside Austin. When David introduces bachelorette 2, a yellow tape marker suddenly appears on the bench in front of the CD player, which promptly disappears in following shots. (Visible on fullscreen DVD.) (00:57:45)
Continuity mistake: At Rhonda's house, when Sam says, "You sure do have a knack for taking something simple and making it beautiful," the red bowl is beside her. After Rhonda shows Sam the white gown, the camera pans back toward the table top and the lace mask suddenly and deliberately appears and is leaning against the bowl.
Continuity mistake: At the start of the pep rally, Mr. Ames takes a seat behind Austin in the close-up. Next shot facing the crowd, when Coach steps up to the stage, Austin's father is gone - his seat is empty, but a couple of shots later Mr. Ames is still there. Additionally, Sam and Carter are also gone in the crowd shot. (01:09:40)
Continuity mistake: When Austin is putting up the "Have you seen Cinderella?" fliers, in one shot he puts up the second flier on the blue door on the lower left side of another flier, but in the following shots, the flier is near the center, then to the right, and then back near the center again. (00:53:05)
Continuity mistake: When Austin is putting up the Cinderella fliers with Ryan and David, his hair is considerably shorter than the following shots, such as when he goes to the diner and talks to Sam at the counter.
Continuity mistake: When Sam is sitting on the friendship circle you can see that her legs are crossed the entire time. When she texts Austin you see her legs and they are not crossed. In the shots before and after this one her legs are crossed. (00:14:50)
Continuity mistake: When Sam is taking batting practice during school, she hits a ball at Carter's feet. If you look at the way she hits the ball, she pops it up. Then the very next pitch she check swings and crushes the ball to Austin Ames.
Continuity mistake: At the beginning of the movie when the younger version of Sam is blowing out her candles, the amount of ice cream in the cup next to her changes within seconds. (00:02:10)
Continuity mistake: When Austin is typing to Sam from his bedroom, the very first book on the shelf in the background keeps changing, over and over again. This occurs near the start, when they are still unknown to each other, and also when he tries to write to her after the pep rally incident.
Continuity mistake: During Sam and Austin's dancing outdoors, Sam's hand shifts. In one shot it is completely over his shoulder and in the next shot it is on his shoulder. We see her hand the entire time so there is no time for her to move it without seeing it.
Continuity mistake: After the twins enter the car wash, in the first shot when Gabriella walks through the vertical black cloth strips, with squeegee in hand, she is wearing the large hoop earrings. When it cuts to the next shot, as she shouts, "Bri?," her earrings are suddenly gone. This occurs before Brianna climbs onto Gabriella's shoulders. (01:04:00)
Continuity mistake: When Sam is running away from Austin at the dance, the bottom of her dress is very dirty, it's almost black. When she runs inside and runs up the stairs, her dress is white again. This is confirmed on the commentary.
Continuity mistake: When Fiona is opening Sam's college envelope she puts a magazine and papers under her arm, but in the next shot there are only papers.
Continuity mistake: When Brianna and Gabriella are in the car wash, they get covered in soap suds. When they fall on top of the car, they are noticeably drier.
Continuity mistake: Right after the twin's swimming instructor says, "Push it ladies," three times, Gabriella reaches for Brianna's hands and grabs them. In the shot right after the fart, Gabriella is still reaching for Brianna's hands.
Continuity mistake: When Fiona picks up the twins at the dance, the rearview mirror on Fiona's Jag disappears on the way back to the diner, but reappears when she pulls into the diner parking lot, then it disappears again. (00:46:45)
Continuity mistake: When Sam and Carter leave the dance and run to the Mercedes so Sam can get back to the diner by midnight, in the long shot before they reach the car we see, one, that Sam pulls off her mask as she's running, and two, there's a rearview mirror on the Mercedes. In the following shots the mask is still on her face, and the rearview mirror has vanished again.
Continuity mistake: When Sam is at Carter's house to give him a lift to school, Carter (in his Snoop Dizzle look) is holding the script in his left hand and the bag's strap falls off his right shoulder when he sits down. Next shot, the script is in his right hand and the strap is back up on his shoulder. (00:11:00)
Continuity mistake: After Sam loses the two parking spaces to Shelby and then Austin, when it cuts to Shelby, Caitlin and Madison walking down the corridor pushing everyone aside, Madison is holding her textbooks with the books' spines facing forward, then facing the opposite way, and finally back again. (00:13:35)
Answer: Yes, this happens in most schools. The reason is that students are more likely to pay attention to announcements that are not made by a boring school employee. In many American schools, we have a phenomenon known as "home room". This is a short period usually first thing in the morning that is non-instructional when announcements are made, forms are filled out, and administrivial functions that don't have anything to do with any one class. At schools that don't have this, they have a thing called "study hall" or "independent study" which is a period where you sit in a classroom and work on your assignments, special functions for the school admin. like you are talking about are frequently done at these periods by students who are "working in the office" rather than studying. Then, there are schools that actually have classes in journalism, broadcasting, etc. where this activity would be part of the schoolwork.
Myridon