[jonbarker]

Montessori uses clear test tube learning devices with beads. Less abstract and more easy to visualize. This is taught in 2nd grade. In your above example, the blank or variable is an empty test tube, the 4 is a tube with 4 beads, and the 9 is a tube with 9 beads.

[PeterisP]

That works well for teaching how to solve problems like that, especially in an early age.

However, do you know what's the Montessori approach to learn abstraction as such, so that you can move from the visual/tangible approach (which works well for simpler problems) to solving problems with the abstract symbol manipulation that's needed for all the more complicated tasks including applied math at physics, economics, etc ?