Some small schools are great, but many can be problematic.
Friendships are often harder, especially for girls seemingly, because the wider potential pool of friends is much smaller, and any fallings-out seemed to grow to affect almost everyone!
Playground politics (parents I mean!) seem to be worse in smaller schools.
Some children like having the same teacher for years, but it's miserable if you don't.
Can be huge culture shock moving to big secondary school - more than the usual culture shock I mean.
My sister in law teaches in a two-class school and she can see more problems than benefits. She says she would never send her own 2 children to one that small.
I would look at each school as a school rather than focusing on size of school. There can be problems with both big and small, and it's easy to generalise.
My children go to a school with 350+ children, but it still feels like a community, teachers who all children well etc, so really I wouldn't make assumptions at all based on size alone.