I'm not completely convinced that small classes are the answer for everyone, tbh. A bouncy extrovert boisterous child, with a good degree of academic ability might find a class of 12 a bit too limiting. Particularly in a mixed school -- I looked at one school recently where the Y6 class of 12 consisted of 9 boys and 3 girls. Pretty tough for the girl who gets left out when the other two team up to be best friends.
Ds is doing fine in Y2 primary class of 32, but the class is quite closely clustered in terms of ability, and he's naturally quite enthusiastic, reasonably hard-working and very sociable. I wouldn't necessarily choose a smaller class for him, though I would like the existing class to have extra teaching support for individual attention.
However, a good friend's dd is in the same class and really struggling -- she's a quirky, quiet little thing, reasonably bright but not naturally good at school work iysim, and has switched off from working because she thinks she's no good at it, and also has problems concentraring. Parents are thinking very hard about moving her to somewhere she can have more individual support, and I can see their point.
And so forth. The permutations are endless, really. I'm shocked by how different my children's needs are, tbh. I assumed they would all just go to the local school, and so far they have, as it happens. But I could very easily make out good cases for each of their needs better being met in different schools if we ran into serious problems.