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.
Visible crew/equipment: As Austin is putting up the Cinderella fliers at school, David tells Austin that he listens to him but promptly gets distracted by a girl. At the start of the next shot, as the girl walks forward the red actor's mark is visible on the floor behind her, where she was standing until she got her cue. (Visible on fullscreen DVD.) (00:53:10)
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.
Visible crew/equipment: When Austin is putting up the Cinderella fliers at school, just as he tells David and Ryan, "The phone's locked. I keep getting messages like...," the red actor's mark is visible on the floor behind Austin and the white actor's T-mark is visible on the floor behind Ryan. (Visible on fullscreen DVD.) (00:53:20)
Visible crew/equipment: At the start of the first scene in the diner, just as we hear Sam begin to say, "At Hal's, everyone felt like family," the actor's green T-mark is visible on the floor, where Eleanor was just standing. (Visible on fullscreen DVD.) (00:01:45)
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)
Continuity mistake: When Sam and Carter arrive at the pool, before Carter reveals himself to Shelby, the poolside gate and banner cast a shadow on the ground, to the right. After Carter is belittled and splashed, when he joins Sam the shadows cast are now longer and farther back. (Visible on fullscreen DVD.) (00:55:15)
Continuity mistake: At school, when Austin is putting up the Cinderella fliers, he tapes the fourth flier on the bulletin board under the word "pep" and over the letters "Fri" in the word Friday. Next shot, the flier has moved to the left, and is taped beside both words "pep" and "Friday". (00:53:30)
Continuity mistake: After young Sam has carried the box of her belongings up to her new bedroom in the attic, she lies down on her bed and as the camera pulls back the window shade is all the way up. It cuts to a wideshot as the camera still pulls back in the rain, and the shade is lower now. (00:05:20)
Continuity mistake: After young Sam loses her father in the Northridge earthquake (noted in voiceover), she appears alone on the ball field, at home plate. In the close-up much of the area is in shadow around her, but in the next wideshot the entire area is in sunlight with only the fence/backstop casting thin shadows. (00:04:30)
Continuity mistake: After the dance, when Fiona and the twins are in the Jaguar, and Carter and Sam are in the Mercedes, all driving to the diner, the views of the side streets they pass change back and forth, between close-ups and wideshots. (00:47:25)
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