Jean Piaget is of the most trusted developmental psychologists in the field of education. He studied the role of biology in the process of learning. Piaget defines the pre-operational stage of development as the stage where a child begins to see herself as a unique individual. Typically, this applies to a child ages 2 to 7. She now uses language for interacting with her peers rather than simply communicating needs for herself. In addition, a child in the pre-operational stage learns the concepts of both conservation (something does not change when it changes shape or consistency) and reversibility (how things conversely relate to one another).
Piaget defines the concrete operational stage of development as the stage where a child solves problems using logical processes. The concept of deductive reasoning, or using cues around him, to formulate answers and thoughts is also what a child in the concrete operational stage can do. Typically, a child ages 7 to 11 falls into this stage of development.
Lev Vygotsky was a developmental psychologist who believed that cognitive development occurs as a result of social development and interaction. Vygotsky's zone of proximal development is the concept in elementary development characterized by the child's ability to complete a certain task on her own versus with a group. There is no specific age range because the concept can be adapted for any elementary aged child depending on her abilities. To create a learning experience based on zone of proximal development, generate a situation where you guide the child through an interactive experience. Depending on the child's current stage of learning, adjust the amount of help you provide the child during the activity.
Vygotsky's internalization process is the idea that the child must make a concept his own using outside experiences. An elementary-aged child progresses through the process of internalization as he develops. This occurs at various rates and can even vary across subject matter. Therefore, the concept is not associated with any specific age range. A child begins the process by taking a situation and then making it his own concept. As the child develops further, he begins to make that concept even more of a personal experience. It is then that the child can reproduce the experience using higher cognitive skills, rather than by straight replication.