During roughly the elementary school years, from about seven to 11, give or take, children move into the third stage of cognitive development according to PAJ. He called this stage the Concrete Operational Stage. Now, we already defined operation, as the ability to figure things out just in ones head. So, this is the primary skill at this age. One of the best examples of this, is how children at this stage can do basic math just in their head. For example, 5 plus 5 is 10. They no longer need to count, add or subtract using their fingers or other objects. Conservation is now possible because of the mental capability of saying something, like, oh. Well, those 2 look different. But I know that that’s really the same. Concrete refers to the fact that children in this stage reason and think about concrete things. Not abstract ones. Abstract ideas and reasoning happen in the next and final stage of cognitive development, Formal Operations, which begins in adolescence.