Education of the senses

"We may conclude with a general rule for the direction of the education of the senses. The order of procedure should be:
(1) Recognition of identities (the pairing of similar objects and the insertion of solid forms into places which fit them).
(2) Recognition of contrasts (the presentation of the extremes of a series of objects).
(3) Discrimination between objects very similar to one another.
- Dr. Montessori's Own Handbook, P. 110