Maturation of the prefrontal cortex allows impulse control, and myelination of the corpus callosum and lateralization of the brain permit better physical coordination. No wonder children move with greater speed, agility, and grace as they age (see Visualizing Development below).

Mastery of gross and fine motor skills results not only from maturation but also from extensive, active play. A study in Brazil, Kenya, and the United States tracked how young children spend their time. Cultural variations and differences based on socioeconomic status (SES) emerged, but at every income level in all three nations, children spent more time playing than doing anything else—including chores, lessons, and conversations (Tudge et al., 2006).

Gross motor skills improve dramatically. When playing, many 2-year-olds fall down and bump clumsily into each other. By contrast, some 5-year-olds are skilled and graceful, performing coordinated dance steps or sports moves.

There remains much for them to learn, especially in the ability to adjust to other people and circumstances. Thus a 5-year-old can sometimes kick a ball with precision, but it is much harder for that child to be a good team player on a soccer team. At every age and skill, physical maturity precedes social maturity.

Many North American 5-year-olds can ride a tricycle, climb a ladder, and pump a swing, as well as throw, catch, and kick a ball. A few can do these things by age 3, and some 5-year-olds can already skate, dive, and ride a bike—activities that demand balanced coordination and use of both brain hemispheres. Elsewhere, some 5-year-olds swim in oceans or climb cliffs. Brain maturation, motivation, and guided practice undergird all motor skills.

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Adults need to make sure children have a safe space to play, with time, appropriate equipment, and playmates. Children learn best from peers who demonstrate whatever the child is ready to try, from catching a ball to climbing a tree. Of course, culture and locale influence particulars: Some small children learn to ski, others to sail.

Recent urbanization concerns many developmentalists. A century ago, children with varied skill levels played together in empty lots or fields without adult supervision, but now more than half the world’s children live in cities. Many of these are “megacities … overwhelmed with burgeoning slums and environmental problems” (Ash et al., 2008, p. 739).

Crowded, violent streets not only impede development of gross motor skills but also add to the natural fears of the immature amygdala, compounded by the learned fears of adults. Gone are the days when parents told their children to go out and play, to return when hunger, rain, or nightfall brought them home. Now many parents fear strangers and traffic, keeping their 3- to 5-year-olds inside (Taylor et al., 2009).

That worries many childhood educators, who believe that children need space and freedom to play in order to develop well. Indeed, many agree that “Environment is the Third Teacher … because the environment is viewed as another teacher having the power to enhance children’s sense of wonder and capacity for learning” (Stremmel, 2012, p. 136).

Observable dangers are not the only reason children are slower to develop skilled gross motor skills. Such skills require practice to develop, but children who breathe heavily polluted air tend to be impaired in brain development as well as to exercise less. Often they also live in crowded neighborhoods and attend poor schools. They have underdeveloped motor skills as well as more learning problems than children living where the air is clean. Are we certain that dirty air impairs their development, or is the cause really something else?

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Scientists have grappled with this question and and found that environmental substances impair brain development in young children at every SES level, especially those in lower-income families. This conclusion is easiest to demonstrate with asthma, which reduces oxygen to the brain. In the United States, asthma is far more prevalent among children who live in poverty than among those who do not (U.S. Department of Health and Human Services, 2012, November). (Developmental Link: Asthma is discussed in Chapter 11.)

As you already know, the dynamic-systems approach to development means that every impairment has many causes, both in the immediate context and in past genetic and environmental factors. Nonetheless, a recent study conducted in British Columbia, where universal public health care and detailed birth records allow solid research, showed that air pollution from traffic and industry early in life was a cause, not just a correlate, of asthma (Clark et al., 2010).

This study began with all births in 1999 and 2000 in southwest British Columbia (which includes a major city, Vancouver). For three years, 37,401 children were studied, 3,482 of whom were diagnosed with asthma by age 3. Each of those 3,482 was matched on SES, gender, and so on with five other children from the same group. Exposure to air pollution (including carbon monoxide, nitric oxide, nitrogen dioxide, particulate matter, ozone, sulfur dioxide, black carbon, wood smoke, car exhaust, and smoke from parents’ cigarettes) was carefully measured.

One finding was that parents could not always protect their children, partly because they did not know when substances caused poor health. For example, although carbon monoxide emissions are not visible, when compared to their five matched peers, those children who were diagnosed with asthma were more likely to live near major highways, where carbon monoxide is prevalent. Conversely, because wood smoke is easy to see and smell, some parents tried to avoid it, but burning wood did not increase asthma.

Respiratory problems are not the only early-childhood complications caused by pollution. Research on lower animals suggests that hundreds of substances in the air, food, and water affect the brain and thus impede balance, motor skills, and motivation. Many substances have not been tested, but some—including lead in the water and air, pesticides in the soil or on clothing, bisphenol A (BPA) in plastic, and secondhand cigarette smoke—are proven harmful.

One recent concern is the contamination from e-waste, a term that includes discarded computers, cell phones, and other outmoded electronic devices. E-waste may spew pollutants that affect the brains of infants and children, although not all scientists are convinced. As one group of researchers explains: “Although data suggest that exposure to e-waste is harmful to health, more well designed epidemiological investigations in vulnerable populations, especially pregnant women and children, are needed to confirm these associations” (Grant et al., 2013, p. e357).

The administrator of environmental public health for the state of Oregon said, “We simply do not know—as scientists, as regulators, as health professionals—the health impacts of the soup of chemicals to which we expose human beings” (Shibley, quoted in T. D. Johnson, 2011). Whether you think Shibley is needlessly alarmist or is simply stating the obvious depends on your own perspective—and maybe on your amygdala.

Lead, however, has been thoroughly researched. There is no doubt that lead is severely toxic. The history of lead exposure in the following A View from Science illustrates the long path from science to practice.

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Fine motor skills are harder to master than gross motor skills. Whistling, winking, and especially writing are difficult. Pouring juice into a glass, cutting food with a knife, and achieving anything more artful than a scribble with a pencil all require a level of muscular control, patience, and judgment that is beyond most 2-year-olds.

Many fine motor skills involve two hands and thus both sides of the brain: The fork stabs the meat while the knife cuts it; one hand steadies the paper while the other writes; tying shoes, buttoning shirts, cutting paper, and zipping zippers require both hands.

Limited myelination of the corpus callosum may be the underlying reason that shoelaces get knotted, paper gets ripped, and zippers get stuck. Short, stubby fingers add to the problem. As with gross motor skills, practice and maturation are key; using glue, markers, and scraps of cloth are part of the preschool curriculum. Puzzles—with large pieces of splinter-proof wood or heavy, smooth cardboard—are essential supplies.

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Traditional academic learning depends on fine motor skills and body control. Writing requires finger control, reading a line of print requires eye control, classroom schedules require bladder control, and so on. These are beyond most young children, so even the brightest 3-year-old is not allowed in first grade.

Slow maturation is one reason many 6-year-olds are frustrated if their teachers demand that they write neatly and cut straight. Some educators suggest waiting until a child is “ready” for school; some suggest that preschools should focus on readiness; still others suggest that schools should adjust to the immaturity of the child, instead of trying to make the child adjust. This controversy is explored in the next chapter.

Fine motor skills—like many other biological characteristics, such as bones, brains, and teeth—mature on average about six months earlier in girls than in boys. By contrast, boys often are ahead of girls in gross motor skills.

Many studies find that fine motor skills correlate with later school performance, which may be one reason that primary school girls typically outperform boys on tests of reading and writing. Although these gender differences seem to be biological, they may be the result of motivation and practice, as young girls are more likely to dress up and play with dolls (fine motor skills), while boys are more likely to climb and kick (gross motor skills) (Saraiva et al., 2013).

Young children are imaginative, creative, and not yet self-critical. They love to express themselves, especially if their parents applaud their performances, display their artwork, and otherwise communicate approval. The fact that their fine motor skills are immature, and thus their drawings lack precision, is irrelevant. Perhaps the immaturity of the prefrontal cortex is a blessing, allowing the creativity without self-criticism.

All forms of artistic expression blossom during early childhood; 2- to 6-year-olds love to dance around the room, build an elaborate tower of blocks, make music by pounding in rhythm, and put bright marks on shiny paper. In every artistic domain, skill takes both practice and maturation.

For example when drawing a person, 2- to 3-year-olds usually draw a “tadpole”—a circle head, dots for eyes, sometimes a smiling mouth, and then a line or two beneath to indicate the rest of the body. Gradually, tadpoles get torsos, limbs, hair, and so on. Children’s artwork is not intended to be realistic: It communicates thoughts and self-expression (Papandreou, 2014). It is a mistake for adults to say “that looks like a …” or worse, “you forgot the feet.”

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Cultural and cohort differences are apparent in all artistic skills. For the most part, Chinese culture incorporates the idea that drawing benefits from instruction, so young children are guided in how best to draw a person, a house, and—most important for the Chinese—a word.

Consequently, by age 9, Chinese children draw more advanced pictures than children of other cultures. Adult encouragement, child practice, and developing technical skill correlate with more mature, creative drawings a few years later (Chan & Zhao, 2010; Huntsinger et al., 2011).

Some parents enroll their preschool children in music lessons, hoping they will learn to play. As a result, those preschoolers become better at listening to sounds, evident in listening to speech as well as music. Neurological evidence finds that their brains reflect their new auditory abilities, a remarkable testimony to the role of family and cultural encouragement of preschool art (Strait et al., 2013).