The "Dinosaurs" puzzle: the child sees the mistake without being told

A wooden inset puzzle: a base board with recesses and a set of dinosaur figures, each of which fits only its own place. The child picks up a figure, studies its outline, finds the matching recess and sets it in.

The key point: error control is built into the board

This property is exactly why such materials found their way into Montessori practice. The figure either fits or it does not — and the child learns the result from the material itself, not from an adult. No need to ask "is this right?", no need to hear "no, not there". That removes the fear of being wrong, and with it the main reason children abandon a task.

This makes the puzzle effective with children who are afraid of mistakes, reluctant to try in front of an adult, or quick to give up after a correction. Here there are no corrections.