What is Montessori– a good, short summary

I often find myself describing what I’ve observed and learned about Montessori education so I liked the summary of Montessori in this Harvard Business Review article (“Montessori Builds Innovators”) taken from Wikipedia:

• mixed-age classrooms, with classrooms for children aged 2½-or-3 to 6 by far the most common,
• student choice of activity from within a prescribed range of options,
• uninterrupted blocks of work time,
• a Constructivist or “discovery” model, in which students learn concepts from working with materials, rather than by direct instruction, and
• specialized educational materials developed by Montessori and her collaborators.