I'm not sure when it started but it took a bit for me to notice, but eventually it boils down to this: Sims repeatedly get up out of their chairs only to go sit down in a different one at the lunch tables in Highschool Years.
While I understand the need for animation and dialogue, this is kind of over-the-top. I would be fine if all the teens ordered lunch and sat down one time, got up one time; but what's actually happening is the teens are repeatedly in the same lunch break changing chairs to talk with their friends (and also not prioritizing eating but that's a separate issue), but the way it happens seems rather...unnatural. Sims should (like humans) be social creatures, but if they are smart enough to sit down and talk at the same time surely you can make it where they don't need to change tables/chairs to talk to everyone in the room? This problem became hyper-focused after a detention bell caused my Teen Sim to nearly be expelled (on the first offense; which was merely being in the lunch room ordering when the bell rang...!), because I was paying extra attention to the screen's timers and such, making sure they didn't get expelled; so some bias is recognized.
On a slightly related note: Musical Chairs is a fun game for kids, you should think about making an official version for child sims.