I was one of 28 pupils at my school. This is in England, at primary level, so covered ages 4 through 11, so I’m not sure how much similarity there’d be with the US system.
First off, it really did break down the cliques- the largest year group was mine, with 6 pupils, but all of us had friends of all ages. There weren’t enough ‘cool’ kids to be able to exclude the ‘not-cool’ ones.
We were divided into 2 main classes, ‘infants’ age 4-7 and ‘juniors’ 7-11, but even between them there was a little flexibility, and there was no real divide within the class.
I’d imagine with 3 teachers, the school would work on a similar principle to mine- instead of being divided strictly by age, we had a situation where all the juniors did the same subject at the same time, but were divided up by level for each subject, on differerent tables in the same room- so you could be taught with the kids the same age for most subjects, mainly with the year above for a few, and with the year below if that was the level you were at. There was stigma attached to being grouped with the younger kids, as it really wasn’t obvious, or seen as majorly important, so long as you were progressing. They’d even have some of the more advanced kids teaching basic concepts to the ones that weren’t getting it.
We actually had a very low problem rate, despite the fact that several of the students were there because the local larger school thought they (or older siblings) were ‘troublesome’- the teachers really did know the kids strong and weak points, in a way that I’d really not found in my previous school (my parents moved 100 miles when I was 8, and I had been at a school with maybe 100 kids previously). I can’t remember any fights, or anyone getting into serious trouble- it got picked up on so early.
As it was so tiny, it was very low budget- we had nothing like the facilities of some of the larger schools, and even trips were very limited, due to there being an awkward number of us- too many for a minibus, not enough for a full-sized bus. We had a deal with the local secondary school that we were allowed to use some of their sports facilities, so we didn’t entirely miss out. We also had a music teacher who came in one day a week, and random arts and science people would do very occasional sessions.
Again, I don’t know how the US system works, but the fact that it was so tiny gave the teachers a lot more flexibility- if a student was really interested in something, the whole class sometimes wound up doing a project on it. There was no formal timetable, apart from when we had visiting or part time teachers in.
For me, it was mainly positive- I much preferred that school to the one of 100 students (still a small school really!), but it would depend on your kid’s personality. There were downsides, and I’d expect a very competetive kid would have found it very boring.