The older kids helped out the younger ones and the teacher walked around the class and talked to each kid to help them along with thier work if they got stuck.
There wasn’t any lecture style teaching with the teacher explaining concepts to the whole class at once.
We all worked on one subject at a time, but we were all at different points in it.
When my family moved and I left that school I was multiple years ahead of where I was supposed to be in several subjects and normal school was very boring after that.
Unless/until we figure out a feasible way to make progress not the same pace for everyone, progress will have to be the same pace for everyone.
Colleges have a decent middle ground where if you fail this quarter, there are decent odds your class will be offered again before next year, especially for the earlier classes that really need stricter sequencing. But that’s only really feasible when you have that many students (not to mention tuition $$$).
I guess in Montessori every single student isn't learning something different, but each one is often in a unique state of learning and development. The guide gives lessons in small groups, less than 6. Each kid gets a new lesson every few days and spends the remainder of their time "doing their work" (practicing their lessons and turning the results into the guide, doing small group research projects, etc.). The kid is encouraged to ask others for help understanding the lesson and to mentor others who are working on a lesson the kid knows. Once the guide observes the kid succeeding at the lesson, the kid is invited to the next lesson.
But the folks making decisions about education in California (including the authors of the California Math Framework 2021) believe they'll achieve better outcomes that way, than they will by grouping students based on their progress in the subject.
I heard recently from a 6th grade math teacher who has students who are 1, 2, 3 and even 4 grades behind.
Imagine orchestrating a single class in which you're teaching some children about adding single-digit numbers, and others about long division.