We have new admin so we'll see. But generally admin decides based on our preferences, our department head's input, a dash of seniority, a healthy spoonful of merit, and their own whims. Unless curriculum change happens, desirable preps only open up when people leave and that's where the decisions are made. Mostly, in my department, they go with my DH's suggestions and she goes based on merit.

I got desirable (AP, IB) preps pretty quickly at my HS but I came in with experience. There are people who were here at the school longer who feel they got "skipped" but they didn't have the content knowledge or parent management skills to impress admin or DH. They see the high level preps as simply "easier" and chill because there's better behavior which is true of Honors maybe but not of any prep higher level than that where you need to push kids to be successful.

Sometimes, you can get stuck in a bad prep by being too good at it. I learned that the hard way at another school and I learned that writing more referrals and failing more kids in a remedial / lowest level class would get me pressured, sure, but if I held strong and excelled with my job in other ways, it would get me less and less of those classes. But many "chill" teachers wonder why they get all the rough kids. They don't want to deal with the paperwork of tons of referrals for every instance it's appropriate per the code of conduct and ruling with an iron fist. So they keep getting what they get because it seems like they're happy enough.

The class no one wants either goes to an extremely mediocre teacher that my DH doesn't care for (she isn't very political -- she likes teachers who do great jobs and dislikes those who phone it in), a really great at working with that class teacher who doesn't assert for themselves and just allows it to happen, or a new hire / teacher with the least seniority (often in the district because my HS considers district seniority more than school).

That's my experience.