And yes, I can see how, in fiction, the lunch period gives these characters a chance to talk, or not talk, when they are not in class. (Also, these kids who eat in the library when they are feeling sad, uh, there was no eating in my school library.) But, I actually think the different folks having different schedules could increase the tension. I think it's a reality that could be used to help. But yeah, try not to have a geography of stereotypes there.
Now, I've asked around, and apparently there are some schools that establish one lunch period for everyone. But, they seem rare. Mostly because students have different schedules each day. My high school had a pretty stable schedule, but there would be lab periods, or assemblies that would change things. My junior year, I had one day that didn't even have a lunch period. I just kept illegal snacks in my locker to tide me over. But plenty of schools have A, B, C, etc schedules where it rotates through a period of days so that all the stuff they need to do can be crammed into the short school day.
I once had someone tell me that if they read another YA that started with the explanation of where all the stereotypes sat in the lunchroom, they would scream. I run into less of them these days, but they were thick on the ground for a while, and while certainly everyone has memories that involve staring at a roomful of people trying to figure out where you should sit, there are things about fictional lunch tables that annoy me. So, here we go.I recognize that in fiction there are often economies. Even in contemporary there's so much world building that throwing in new people every chapter is too much, so while the character may be at a school with hundreds of students, there will likely be 10 or less that get names and character traits. That's fine. But, everyone always has the same lunch period. And that, never happened to me. There were usually people I liked or was happy to hang out with my lunch period, but all of my friends, all getting the same lunch period, every day? Nope. Never happened to me.