Setting the Context

Childhood comprises two phases—early and middle childhood—and this period of life lasts longer in our species than in any other animal. We need this time to absorb the lessons passed down by previous generations, and to take advantage of our finely tuned ability to decode intentions—the talent that has allowed us to advance. The frontal lobes, in particular, take two decades to become “adult.” As this region of the brain—involved in reasoning and planning— develops, every childhood ability improves.

Physical growth slows down after infancy. Girls and boys are roughly the same height during preschool and much of elementary school. Boys are a bit more competent at gross motor skills. Girls are slightly superior in fine motor skills. Although preschool fine motor skills predict elementary school success, we need to be careful not to push young children too hard. Undernutrition severely impairs motor skill development by making children too tired to exercise and play.

Rates of childhood obesity—defined by a high body mass index (BMI)—dramatically increased starting about 40 years ago, although the prevalence of this epidemic differs across nations and in specific demographic groups. While the main general cause for this modern scourge lies in toxic environmental forces (too little exercise, an abundance of tasty, calorie-dense foods, and so on), children differ genetically in their tendencies to be overweight, and the best predictor of later obesity is rapid weight gain early in life. Because prejudices against overweight children are intense, parents tend to minimize their children’s weight issues and can be reluctant to participate in family interventions. Rather than just changing society, it’s important to discourage overfeeding babies and decode the biochemical conditions causing vulnerable infants to gain excessive weight.

Piaget’s preoperational stage lasts from about age 3 to 7. The concrete operational stage lasts from about age 8 to 11.

Preoperational thinkers focus on the way objects and substances (and people) immediately appear. Concrete operational thinkers can step back from their visual perceptions and reason on a more conceptual plane. In Piaget’s conservation tasks, children in preoperations believe that when the shape of a substance has changed, the amount of it has changed. One reason is that young children lack the concept of reversibility, the understanding that an operation can be repeated in the opposite way. Another is that children center on what first captures their eye and cannot decenter, or focus on several dimensions at one time. Centering also affects class inclusion (understanding overarching categories). Preoperational children believe that if something looks bigger visually, it always equals “more.”

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Preoperational children lack identity constancy—they don’t understand that people are “the same” in spite of changes in external appearance. Their thinking is characterized by animism (the idea that inanimate objects are alive) and by artificialism (the belief that everything in nature was made by humans). They are egocentric, unable to understand that other people have different perspectives from their own. Although Piaget’s ideas offer a wealth of insights into children’s thinking, he underestimated what young children know. Children in every culture do progress from preoperational to concrete operational thinking—but the learning demands of the particular society make a difference in the age at which specific conservations are attained.

Lev Vygotsky, with his concept of the zone of proximal development, suggested that learning occurs when adults tailor instruction to a child’s capacities and then use scaffolding to gradually promote independent performance. Education, according to Vygotsky, is a collaborative, bidirectional learning experience.

Information-processing theory provides another perspective on cognitive growth. In this framework on memory, material must be processed through a limited-capacity system, called working memory, in order to be recalled at a subsequent time. As children get older, their working memory-bin capacity dramatically expands, which may explain why children reach concrete operations at age 7 or 8.

Executive functions—the ability to think through our actions and manage our cognitions—dramatically improve over time. Children adopt learning strategies such as rehearsal. They get better at selective attention and inhibiting their immediate responses. The research on rehearsal, selective attention, and inhibition provides a wealth of insights that can be applied in real life.

Attention-deficit/hyperactivity disorder (ADHD), the most common childhood disorder in the United States, involves impairments in executive functions such as working memory, inhibition, and selective attention, and presents widespread problems at home and school. This condition, usually diagnosed in elementary school (more often among boys), can have a bewildering array of pathways and possible brain causes. Treatments involve medication, training for parents and children, dietary interventions, providing white noise, exercise, and high-intensity games. The dramatic rise in contemporary Western ADHD diagnoses could be partly a product of a poor child-environment fit.

Language makes every other childhood skill possible. Vygotsky believed that we learn everything through using inner speech. During early childhood, language abilities expand dramatically. Phonemic (sound articulation) abilities improve. As the number of morphemes in children’s sentences increases, their mean length of utterance (MLU) expands. Syntax, or knowledge of grammatical rules, improves. Semantic understanding (vocabulary) shoots up. Common language mistakes young children make include overregularization (using regular forms for irregular verbs and nouns), overextension (applying word categories too broadly), and underextension (applying word categories too narrowly).

Autobiographical memories, the child’s understanding of having a personal past, is socialized by caregivers through past-talk conversations, questioning young children about shared life events. Specific autobiographical memories consolidate into a coherent identity during the teens. Overly general autobiographical memories (or not recalling salient events from the past) may indicate a child’s having an abusive early life.

Theory of mind, our knowledge that other people have different perspectives from our own, is measured by the false-belief task. Children around the world typically pass this milestone at about age 4 or 5, although the roots of this uniquely human ability appear before age 1. Cultural forces, being bilingual, having older siblings, and having parents’ continually talk about people’s mental states predict the emergence of this vital skill.

Autism spectrum disorders (ASDs), characterized by severely impaired social skills and abnormal repetitive behaviors, are emblematic of impaired theory of mind. These devastating disorders, which typically are diagnosed in early childhood, are rising in prevalence, and have unknown causes.