And I think that the major cause of this is parents' pressure. I experience it myself (also 16yo) and I see my classmates experience it to. Example: A group of us are doing a CAS project (required for the IB diploma) and we'd formed a group of boys. Before we finalised our group, one of the guys said (I kid you not) that his parents told him that having a girl on the group would help him on college apps. I wasn't opposed to the idea, but the motivation was clear: he didn't want to do it for diversity of opinion, he wanted to do it because his parents said so. And the attitude of the kids extends to how they perceive others. There's almost a hierarchy of students in my school: the ones that aspire to first-tier, second-tier, and so forth, to community college at the lowest step on the ladder. Students in the higher steps have internalised what they've been told about the college apps process, and scoff when someone suggests that maybe the community college or state college route is best, so that you're not saddled with student loan debt.

With regards to smartphones, I find that I have almost the opposite experience. My high school has the same three tiers as yours: IB/AP, Honors, regular classes. I find that smartphone use is generally the same across classes, yet it is done more openly in regular classes, under the table in Honors, and in the IB/AP classes, they resort to using their smartwatches to type (generally because the IB/AP kids are richer, another bad part of high schools in the US).

Also, wow. Your school doesn't have anyone dating? In my school there are many carnal relationships among students who take the regular classes.

Yes, and this is why it is hard for those (like me, HS student, 16yo) who avoid social media as a matter of privacy. I personally get left out of friend groups, etc. and when I was applying for an internship, one of the questions was "Please list your social media handles/accounts here"... I'm pretty sure I know why I didn't get that internship :) They probably thought I was hiding something...