To a child, things are fair when everyone gets the exact same thing.
A mature definition of fairness is when everyone gets what they need depending on who they are and where they are at.
It’s interesting that most schools are managed and created by adults who choose to look at the child’s way of interpreting fairness.
We’re visiting family in Colorado, nursing my dad back to health after back surgery. His kids are the same age as mine (9, 6 and 6) and there has been a lot of talk about how things aren’t fair. Part of learning around kids that are different ages is that kids learn that fairness is not just about everyone getting the same thing at the same time. And part of learning in a zen-schooling or unschooling environment, where everyone gets what they need when they need it, instead of when the adults around them think they need it, is that kids (and parents) learn, and live, the mature definition of fairness.