A. Operational Stage (ages 7 or 8-11 or 12 years)
Key feature of this phase is the development of the children have started to use the rules are clear and logical, and the mark of reversible and eternity. Child has the capability to think logically, but only with objects that are concrete. Operation is an object of type action to manipulate picture is in him. Because this activity requires a process of transformation into itself so that more effective action. Children have no need to try and make a mistake, because the child is able to think by using the model of'' likely'' in performing certain activities. He can use the results that have been achieved before, children are able to handle the classification system.
B. Formal Operational Stage (11/12-18 years)
Key feature is the development at this stage the child is able to think abstract and logically by using the pattern think the'' possibility''. Modele with the type of scientific thinking and inductive hiphotetico have already started in children, with the ability to draw conclusions, interpret and develop hypotheses. At this stage children are able to think of the condition:
1) Work effectively and systematically.
2) Analyze the combination, thus has been given two possible causes. For example, C1 and C2 yield R, the child can formulate a few possibilities.
3) Thinking proportionally, determining the proportional variety of C1, C2, and R for example.
4) It is interesting generalization is fundamental to a range of content. Piaget believed that most teens reach formal operations not later than at age 15. But based on the research and subsequent studies found that many students even though students have exceeded the age, can not do formal operationts.
