The standard Peninsula path looks like this: a daycare at two, a preschool at three, a public kindergarten at five, sometimes a different elementary after that. Four settings before nine years old, each with its own routines, expectations and social order to work out.
What a transition actually costs
Roughly a term, every time. Not of academic content — of the invisible work of learning how a place runs, who to ask, what is allowed. Young children do this well, but they do not do it for free, and the cost is paid in the settling weeks when they are not learning much else.
The specific Montessori version of the problem
It is sharper here, because the method is cumulative. A child who has spent four years learning to choose their own work, plan a morning and finish what they start walks into a traditional first grade where none of that is wanted. The habits are not merely unused; they have to be actively replaced.
What continuity looks like instead
One building from age two to eleven. The same method throughout. A fourth-grader who started in the toddler room and a two-year-old sibling who is starting now, both dropped off at the same door at the same time. Families with two children of different ages do one run, not two.
It is the reason most families end up at Mills rather than somewhere closer — almost every other Montessori school within reach of South San Francisco stops at kindergarten.