The work for deep knowledge
When you let your child exploring the word with his hands, there is a process that Montessori observed that is really underestimated.
In The Advanced Montessori Method, she explains how a simple manipulation of counts with hands can teach children foundation math concepts like areas and exponentiation. This is really interesting.
For a layman, just watching the children taking action with the Montessori resources, the process is not understood in terms of the learning.
The method is really careful for the learning.