Montessori Geometry Three-Part Cards for Impressionistic Lessons on Points, Lines, Planes, Surfaces, and Solids. In the Montessori method, children aged six and above begin their geometry education by exploring the fundamental concepts of point, line, plane, surface, and solid. These concepts are then explored in more detail in a sequence of lessons that build on each other. The sequence may vary from child to child, but the work in each area progresses logically. Here are some definitions of th