Montessori addition strip board.
Number is all around us, even from birth.  Montessori's carefully developed mathematics sequence presents mathematical concepts in a concrete way, moving increasingly towards the abstract. 

A thorough introduction to the Montessori math methods and activities can be found on the AMI Primary Guide page on mathematics.  The following videos show first an overview of the mathcurriculum, then demonstrations of the presentation of two math activities: sandpaper numbers and the spindle box.