We looked at ~100 kids per grade and only a single large school 300 ish per grade.
Well my older kid deliberately wanted a smaller school. Loved the idea of tiny classes and getting to know people in a community. Also liked the idea of being able to try everything ( without everyone already being an expert in that field). The thing with a small school is, teachers really get to know the kids. Opportunites are roughly the same in terms of kids going to things like Science fairs, or Championships but with a smaller number of kids, your kid will get picked more often. A good example is sport. My kid took up a sport, was immediately in Varsity and went to some high level regional meets. Would not have happened in a larger school. It’s not even my kids’ main sport. And if kids are stellar coming into 9th grade, they can shine for 4 years not 1.
Younger kid liked the idea of a larger school. Wanted to jump into having more odd classes and even odd languages available. The idea of kids being good in a sport and recruited wasn’t an issue as kid is a great athlete in one sport. But it was also an issue of being top on the team and being low ranked for a few years. Very different. Also, theatre. At one school, the likelihood of being a lead in a play was low ( some kids are pre-professional when they get to the school) or pretty good. Again, do you want to be really strong in a single field ( or two) or be into everything?
We often thought that BS should be 150 kids. But few were. The 150 would allow for a large enough class to accommodate a wide range of kids but not be too large.
Small size plus: Know everyone, more opportunities for all, might be easier for introverts, community+, tiny classes in specialized subjects. Also some small schools might have the ability to make your own class and learn alongside a specialist or teacher. This can fill in the gap if your kid wants to study something really specific. Can join most clubs, teams, events you want. You can be a leader in multiple areas. You can also excel in multiple fields. You have the ability to try new things in high school and excel at them.
Cons: Athletic teams can be less competitive, all teams might be less competitive as there are fewer kids to apply. Can be fewer kids who are similar. You might not have enough kids to do unusual activities.
Large Size plus: Building and classrooms tend to be more impressive. The theater is larger, the track is bigger, the classrooms might be nicer. Campus is larger ( might be positive or negative). Might be easier to find people like yourself.
Large size cons: Kids can be anonymous ( get lost). Might/might not happen. Might not be able to get into that great class because it’s full. Might not be able to represent your school at an event because it’s Juniors/Seniors only or your skillset isn’t good enough. At the top schools, kids are stellar. So when you run track you are running against kids who will likely go Div I. Or when you are on the debate team some might be doing that as their only activity. If a kid is really into a single sport or thing, a large school can be an easy on ramp.
We find the small school vs. large school issue not to be specific to BS. If our kids had gone to the large public school, the issues would have been the same. Their peers have confirmed that there are X kids and Y kids but few kids who do multiple things equally well across fields.