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: 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.
Other mistake: During the pep rally scene, when Shelby is staging the play, Gabriella comes out wearing a bridal gown. A couple of seconds later, she comes out wearing the "diner girl" outfit, complete with roller skates. There was not enough time for her to change so quickly.
Factual error: Toward the end of the movie just as Austin and his team start the football game, the camera shows the scoreboard counting down from 15:00 minutes, the problem with this is high school football games are played in 12:00 minute quarters not 15:00.
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.
Revealing mistake: In the beginning of the dance scene, when Sam gives Carter her phone so he can set the alarm, the phone isn't even on when he is programming it.
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.
Visible crew/equipment: When Rhonda's in the kitchen with Bobby, and she tells him that it's enough with all the salmon dishes, as the camera zooms in we can see the crew member (wearing a pouch at his hip) with his arm up, at the left of the screen, as he's presumably holding up the boom pole and mic.
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.
Audio problem: When Hilary Duff is Text Messaging her "Secret Admirer" the sounds of her pushing the phone's buttons don't match up with her fingers pushing the buttons.
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: At the start, when Sam is at school and texts "We talked this morning", her cell antenna is pulled out, but next shot the antenna is suddenly back in, though Sam's hands are in the same place.
Factual error: During the opening credits, as Hal and 9 yr old Sam are driving down the street they pass several 2004 cars, including a Chrysler convertible. However, the opening scene takes place before the '94 Northridge earthquake, which is specifically noted in Sam's voiceover during the earthquake, and 8 years prior to the rest of the '04 film.
Visible crew/equipment: While Sam tries to beat Fiona back to the diner, Fiona and her girls walk into the diner, and when Fiona walks behind the counter, the actor's white T-mark is visible on the floor under the counter, in front of Eleanor's skates.
Continuity mistake: When Rhonda tells Fiona that she is going to find a place to put her six dollar pedicure, she puts her hand on the counter. In the next shot (from the back), her hand is down by her side.
Continuity mistake: When Sam and Austin are talking about Princeton (through chatting and voiceover), Sam asks Austin if he's told his dad that he wants to go to Princeton, Austin types "He's got a whole other plan." but he says "He HAS a whole other."
Visible crew/equipment: The camera and a crew member can be seen in Gabriela's car when she is practicing her "speech" at the gas station.
Continuity mistake: In the first shot of the scene with Gabriella and Brianna talking with Shelby and her friends, convincing her that Sam tried to steal Austin away from her, Brianna is sitting with her arms folded on the table, but in the next shot, she's holding a tissue (which was not present in the previous shot) right before she says "Our stepsister has always been jealous of you" and blows her nose. (Visible on fullscreen DVD).
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