Attachment: the emotional bond that forms between an infant and caregiver(s), especially parents. (Hockenbury, 361) An emotionally important relationship in which one individual seeks proximity to and derives security from the presence of another, particularly infants to parental figures. (Collin, 340)

Cognitive Development: a learner’s acquisition of facts, concepts, and principles through mental activity. (Johnson, 72) The evolution of an individual's problem solving skills, memory, language development, and ability to process information about their environment. (NCIt)

Critical Period: period during which a child is maximally sensitive to environmental influences. (Hockenbury, 351) A specific stage in animal and human development during which certain types of behavior normally are shaped and molded for life. (MeSH) Important period in a human’s development during which it is especially plastic and sensitive to the environment, and during which it has rapid, formative growth. For example,  'language development' – infancy to between 8 years and puberty start. After this critical period closes, a person’s ability to learn a second language without an accent is limited. Second languages learned after the critical period are not processed in the same part of the brain as is the native tongue. Each neural system has a different critical period. (Doidge, 51) In infancy, and progressively staged across those higher and higher brain levels through childhood, plasticity goes through a critical period, a time of riotous brain change. Through the critical period, each functional zone of the brain is remodeled to make its own special contribution to that long, slow process of creating, an effective, operational person. (Merzenich, 45)

Object Permanence: the understanding that an object continues to exist even when it can no longer be seen. Infants acquire this by the end of the “sensorimotor stage” (about 2 years of age). (Hockenbury, 369)

Ratios: the ratio of children to caregivers. According to a study by the National Association for the Education of Young Children, two caregivers should care for no more than 8 infants, or no more than 12 toddlers, or no more than 20 four and five year olds. (Hockenbury, 362)

Social Development Theory: argues that social interaction precedes development; consciousness and cognition are the end product of socialization and social behavior. (LearningTheories, 18) (Developed by) Russian psychologist Lev Vygotsky. He saw human development taking place on three levels - cultural, interpersonal, and individual. He believed that teachers should play an instructive role, constantly guiding and nurturing their pupils in order to improve their attention span, concentration, and learning skills, and so build up their competence. This idea had a marked effect on education in the late 20th century, stimulating a shift from child-centered to curriculum-centered teaching. (Collin, 270) The belief that the human mind develops from the interactions between people and society. Social development plays a key role in the development of cognitive processes. A person (exists) with a higher level of understanding than the learning individual, (for example) teachers, adults, or a coach. Their exists a “zone of proximal development.” (Kleinman 263)

Zone of Proximal Development: the difference between what children can accomplish on their own and what they can accomplish with the help of others who are more competent (Hockenbury, 373) The distance between the ability of the person that is learning under the guidance of another person and the ability of the individual to solve the problem on his or her own. (Kleinman, 263-264)

Stages of Development: stage of the human lifespan defined by age. Most physical, mental, and social changes occur gradually. (Hockenbury, 351)

Adolescent: a person 13 to 18 years of age. (MeSH) Development stage where we develop a coherent sense of who we are, through consideration of our past, present, and future. When successfully negotiated, this stage ensures a unified sense of self. (Collin, 272)

Child: a person 6 to 12 years of age. An individual 2 to 5 years old. (MeSH) A person who is not yet an adult. The specific cut-off age will vary by purpose. (NCIt) (Developmental stage where) children focus on education and learning social skills. It provides a feeling of competence, although an over-emphasis on work can lead children mistakenly to equate self-worth with productivity. (Collin, 272)

Infant: a child between 1 and 23 months of age. (MeSH) Trust vs. mistrust stage of development. If the infant’s needs are badly or inconsistently met, feelings of mistrust develop that can recur in later relationships. The child learns to explore, but also for the first time must deal with feelings of shame and doubt as a result of small failures or parental reprimands. Healthy will power develops as a result of learning to negotiate both success and failure. (Collin, 272)

Tabula Rasa: Latin word meaning a tablet from which the writing has been erased, ready to be written on again. A clean slate; a mind having no innate ideas. (Oxford) Researchers for decades thought that babies were a tabula rasa. They thought that everything a baby knew was learned by interactions with its environments, primarily with adults. We know better now. (Medina, 264)

Temperament: inborn predispositions to consistently behave and react in a certain way. (Hockenbury 358) Predisposition to react to one's “environment” in a certain way; usually refers to mood changes. (MeSH) An individual's habitual frame of mind or natural emotional disposition. (NCIt)