lateralization: Literally, sidedness, referring to the specialization in certain functions by each side of the brain, with one side dominant for each activity.

centration: A characteristic of preoperational thought in which a young child focuses (centers) on one idea, excluding all others.

symbolic thought: In preoperational intelligence understanding that words can refer to things not seen and that an item, such as a flag, can symbolize something else (in this case, a country).

myelination: The process by which axons become coated with myelin, a fatty substance that speeds the transmission of nerve impulses from neuron to neuron.

hippocampus: A brain structure that is a central processor of memory.

corpus callosum: A long, thick band of nerve fibers that connects the left and right hemispheres of the brain and allows communication between them.

animism: The belief that natural objects and phenomena are alive in the way that humans are, as in a rock having emotions and a spirit.

preoperational intelligence: Piaget’s term for cognitive development between the ages of about 2 and 6; it includes language and imagination (which involve symbolic thought), but not yet logical, operational thinking.

egocentrism: Piaget’s term for children’s tendency to think about other people and their own experiences as if everything revolves around them.

hypothalamus: A brain area that responds to the amygdala and the hippocampus as well as various experiences to produce hormones that activate other parts of the brain and body.

focus on appearance: A characteristic of preoperational thought in which a young child assumes that the visible appearance of someone or something is also their essence.

impulse control: The ability to postpone or deny an immediate response to an idea or behavior.

amygdala: A tiny brain structure that registers emotions, particularly fear and anxiety.

perseveration: The tendency to persevere in, or stick to, one thought or action for a long time.

executive function: The cognitive ability to organize and prioritize the many thoughts that arise from the various parts of the brain, allowing the person to anticipate, strategize, and plan behavior.

theory of mind: A person’s theory of what other people might be thinking. Children gradually realize that other people do not always know and think what they themselves do.

Montessori schools: Schools that offer early-childhood education based on the philosophy of Maria Montessori, which emphasizes careful work and individualized accomplishment.

Reggio Emilia: A program of early-childhood education that originated in the town of Reggio Emilia, Italy, and that encourages each child’s creativity in a carefully designed setting.

Head Start: A federally funded early-childhood intervention program for low-income children in the United States.

theory-theory: The idea that children attempt to explain everything they see and hear by constructing theories.

scaffolding: Temporary support that is tailored to a learner’s needs and abilities and aimed at helping the learner take the next step in learning something.

pragmatics: The practical use of language, adjusting communication according to audience and context.

overimitation: When a person imitates an action unnecessarily. Overimitation is common among 2- to 6-year-olds when they copy adult actions that are irrelevant and inefficient.

static reasoning: A characteristic of preoperational thought in which a young child thinks that nothing changes. Whatever is now has always been and always will be.

overregularization: Applying rules of grammar even when exceptions occur, making the language seem more “regular” than it actually is.

zone of proximal development (ZPD): In sociocultural theory, a metaphorical area, or “zone,” surrounding a learner that includes all the skills, knowledge, and concepts that the person is close (“proximal”) to acquiring but cannot yet master without help.

mentor: Someone who teaches or guides someone else, helping a learner master a skill or body of knowledge.

conservation: The principle that the amount of a substance remains the same (i.e., is conserved) even when its appearance changes.

fast-mapping: The speedy and sometimes imprecise way that children learn new words by quickly categorizing them.

irreversibility: In preoperational thought, the idea that change is permanent, that nothing can be restored to the way it was before a change occurred.