What distinction can be made between the preoperational stage of development and the concrete operational stage?

Piaget explained four stages of development: sensori-motor, preoperational, concrete operational, formal operational stages.

Preoperational stage happens at the ages from 2 to 7. At this stage, children become skilled, but they still think concretely.

Concrete operational stage happens form ages of 7 to 11 years. At this age, children start thinking logically.