There are some ideas that are so ingrained in our society it is sometimes hard to remember that at some point someone had to create that idea. One of the keystones of modern teaching and parenting is the idea of stages, and while many of the stages that are spoken of in this way are not originated by Jean Piaget's cognitive development theory the idea of stages is largely because of him¹.
In Piaget's theory there are four stages of cognitive development². The first stage beginning at birth and the last beginning at adolescence. The importance of this idea is that a child who is not advanced enough to learn an idea will find it impossible to learn the idea, and it will be very frustrating for both student and teacher. It is also worth noting that developmental stages are not based on intelligence and going through these stages earlier or later than expected means only that they are physically developing slower.
The first of Jean Piaget's stages is sensori-motor. This stage begins at birth and goes until about two. At this age children learn how to do basic motor skills. A child at this age is simply learning the basic skills. If you want to teach a child at this age it should be through sensori-motor factors. Explaining them will generally not work, but tone or a frown can.
The second stage, pre-operational, begins about the age that the child begins to talk and continues until the child is about seven years old. At this age a child is able to use symbols. Children of this age generally give personalities to objects, especially toys. They are also far more likely to have fantasies and have difficulty with the difference between that fantasy and reality and difficulty with time.
Around the age of seven until adolescence is the concrete stage. At this age children will begin to learn in the more traditional and rational manor but they still often have difficulty with abstract ideas. For example children of this age will find math far easier when using real objects rather than simply numbers. At this age, they will often want to ask a lot of questions about very specific things,
The fourth stage is called formal operations and begins in adolescence and continues through the rest of life. At this age, people should be able to understand abstract ideas and critical thinking. They should also be able to understand things from other peoples' perspectives.
There are many ways to look at how personalities develop, but one of the most time-honored of them is Piaget's Cognitive Stages and whether it is still the most accurate way to describe childhood development it is too important to ignore.