Barbel Inhelder & Jean Piaget 
Child’s Conception Of Geometry [PDF ebook] 

This is Volume XIX of thirty-two in a series on Developmental Psychology. Originally published in 1960. There are certain problems of a general nature in regard to the development of spatial concepts in young children, the problem of spatial intuition as a whole is exceedingly complex, and this study discusses of a child’s conception of geometry of measurement and metrical geometry.