Absolutely agree with Blueberry that small primaries are incredibly dependent on the quality of Teachers/HT.
IME one DC may get a brilliant education and another a mediocre one at the same school.
With split years, maternity leaves and illness, a child may get teachers who understand them and differentiate work to their abilities or they may not.
One child's journey through primary may be very different to another's. Two years with a teacher who's class room management isn't great if you have a easily distracted child with a noisy cohort. The same teacher with a quieter cohort might be fine.
The same goes for performance at secondary. Some teachers and some subject leaders are way better than others, some classes behave appallingly. While the same teacher may get good results elsewhere.
Yes good school wide discipline and strong leadership helps, but even the very best HT can't stop some children and some teachers just not gelling. They can't stop teachers getting ill. They can't recruit brilliant MFL teachers when non apply. They can't expel trouble makers before they damage other children's learning.
In any case often the 'trouble makers' need support not sanctions, that most schools simply can't provide.