5 ideas
Didactic materials like the graduated cylinder blocks are designed so that a mistake makes the task physically impossible to finish, such as a cylinder left over or one that will not fit. The child therefore detects and corrects their own error without an adult pointing it out, which moves the source of correction from the teacher to the material.
Montessori argues that children held still at fixed desks and moved by rewards and punishments display only suppressed, artificial behavior. Because of this, a pedagogy that claims to be scientific must first let the child act freely within limits, since only spontaneous activity reveals the child's real nature and can be studied at all.
The teacher's main job becomes watching and recording the child's spontaneous activity, the way a scientist watches natural phenomena, and stepping in minimally. The teacher prepares the environment and demonstrates briefly, then withdraws, and judges success by how little they need to intervene.
Each sensory material varies only one attribute, such as weight, color, texture, dimension or pitch, and keeps every other attribute constant. That lets the child focus attention on a single difference and sharpen discrimination along it. Lessons follow a three-period sequence: naming ("this is rough"), recognition ("give me the rough"), and recall ("what is this?").
If children first trace sandpaper letters with their fingers and practice controlled pencil strokes with metal insets, the motor and sound-shape skills of writing develop separately and in advance. At around four or five the child then begins writing suddenly and all at once. Writing comes before reading because it is built from mechanisms the child has already mastered.