The children in the above picture are working with the Spindle Boxes. The children are placing the appropriate number of spindles in each box, #s 0-9. They seem to enjoy opening an empty hand over the #0 box and physically feeling how full their hands get as the numbers increase. Like many Montessori materials, there is a control of error. If the child/children have 9 spindles left at the end, they have most likely done the work correctly. If not, they recognize there is a problem, count again and correct themselves.