Within the realm of psychology, the "concrete operational stage" refers to the period of child development, generally occurring between the ages of seven and eleven, when children develop the ability to think in terms of concrete concepts using inductive reasoning, but still lack the ability to understand more abstract concepts.
The concept of the concrete operational stage was developed by Jean Piaget(1896-1980) in his studies of child development. As Piaget theorized, there are four main stages in the average child's mental development. The first stage is the "senorimotor stage," which involves the learning of basic motor skills from birth to age two; the second stage he labeled the "preoperation stage," which occurs between the ages of three and seven and involves development of the ability to use language and to think in terms of symbols; the third, the "concrete operational stage," is when cognitive development occurs involving the use of logic; and the fourth and final stage he called "formal operations," and involved children between 12 and 15 learning to think and understand abstract concepts.
Piaget's observations of children, particularly his own, enabled him to conduct various benign experiments to determine what children are capable of at different phases of childhood: how they approach simple and increasingly complex tasks, and how they reason. The concrete operational phase, as described in the eNotes biography of Piaget to which a link is provided below, is the crucial stage of mental development when children learn to distinguish between objects and concepts, albeit only those for which the meaning is elementary. Despite that limitation, children learn problem-solving and how to think logically, thereby making this stage a particularly crucial one for mental development.