Choices 

In Montessori, the children themselves make choices as to what they will work with on a given day; in public/parochial school the teachers decide. Therefore, in Montessori, a child who has intense interest in multiplication (perhaps the multiplication process is finally making sense!) is able to spend extended periods of time absorbed in multiplication exercises of his choosing.

In public/parochial school that enthusiasm must be contained until the period arises in which multiplication is offered, and even then the child can only do those exercises which the whole class is working on and only for the period within which the class is doing them.