This chapter contains an integrative framework of the seven themes that have emerged throughout the book.

Theme 1: Nature and nurture: all interactions, always

If prenatal development proceeds normally, it seems as if it is simply the development of innate potential in which the environment is not important. However, if things go wrong, it is obvious that nature and nurture interact. Consider, for example, teratogens, harmful substances the child can get in contact to in the womb. The extent to which negative effects occur depends on genes and other environmental factors, such as timing.   

A certain nature also evokes a certain nurture. For example, babies that are cute, motivate people in the environment to play and interact with them. Timing is also important, normal development of certain skills is only possible when a child is exposed to relevant experiences during a specific period. If this does not happen, developmental retardation can arise in terms of perception, language, intelligence, emotions and social behavior.   

Many genetically influenced characteristics only emerge during later childhood, adolescence or adulthood. Think of the physical changes that occur during puberty, or the development of nearsightedness in later childhood or early adolescence. Schizophrenia also often manifests itself later. In all these characteristics, an interaction between nature and nurture is also important.

All in all, it seems like everything affects each other. Genes, traits and behavioral tendencies interact with the nurture that children receive in different ways. In this way self-image, intellect, actions and other qualities arise.

Theme 2: Children play an active role in their own development

Even before birth, children learn to distinguish between different stimuli and when they are born, they are already able to selectively focus on certain interesting objects. Their actions also elicit reactions from other people, which further shapes their development. This ability to interact with the environment is greatly enhanced during the first year of life. The children learn to follow moving objects with their eyes, and they learn how to crawl which helps to actively explore the environment. As the development continues, children learn to talk and practice when there is no one around to hear it. Later they learn to start conversations which helps to obtain information and in which they can express their feelings. When a bit older, the choices of the child with regard to their friends determine whether they will be inclined to show criminal behavior, to drink or to use drugs.

Already during the first year of life, children develop a feeling of all the possibilities in the physical world. This indicates a desire to understand the world, motivating children to formulate informal theories regarding objects, living things and people. Characteristics of the child determine how they interpret an event and how they respond to it. So, both subjective interpretations and objective reality influence the development. 

The regulation of behavior also contributes to the development. In the first months of their lives, children are completely dependent on the caregiver to regulate their emotions. Later they learn ways to deal with it themselves. At first it is physical (for example looking away), but at primary school children learn to use cognitive strategies and discuss their problems with friends. The children's way of decision making has a strong influence on their future life.

Children elicit reactions from the people in their environment. Attractive babies cause more positive reactions and are often more affectively and playfully mothered than less attractive babies. Later on, interests and skills begin to influence the interactions. Children who are contrarian and aggressive can cause the parent to avoid confrontations and increasingly give in to the child, creating a negative spiral. Children who are cooperative, friendly and social are often more popular among their peers than children who behave aggressively.  

Theme 3: Development is both continuous and discontinuous

It seems that many individual differences in psychological characteristics are reasonably stable over the entire development, but this stability is far from 100%. An example is intelligence. Stability of intelligence increases as the child grows older, but even at a higher age the IQ varies slightly from situation to situation. Personality characteristics also seem fairly stable over time: shy toddlers grow up to shy children, aggressive children to aggressive adolescents, and so on. But regardless of whether the focus is on intellectual, social or emotional development, stability is influenced by the environment.

Many of the most prominent development theories divide the development over different stages (think of Piaget, Freud, etcetera). These stage theories have a number of things in common:

Development proceeds according to a number of qualitatively different stages.

When children are at a certain stage, a wide range of thoughts and behaviors reflect the characteristics of that stage.

The stages follow each other in the same order for all children.

Transitions between stages happen quickly.

However, development is much less organized than these stage theories implicit. There barely happens a sudden change in a wide range of tasks and skills. Often there is a continuous increase in certain skills, but this does not mean that there is no sudden developmental jump in certain specific areas. These sudden jumps could be attributed to certain underlying, continuous processes. Whether a process is seen as continuous or discontinuous depends on where the focus lies. Making statements about when a certain competence arises can therefore be quite arbitrary but mapping the milestones in the development can give an idea of ​​how far a child is.   

Theme 4: Mechanisms of developmental changes

According to Piaget, development proceeds through the interaction of assimilation and accommodation. Through assimilation children interpret new experiences in terms of their existing mental structures. By accommodation they review existing mental structures according to new experiences. From this theory we have learned a lot about development mechanisms on biological, behavioral and cognitive levels. 

The genotype determines a rough outline of the development, but the details are filled in by the interaction between genotype and environment. The complexity of the changes on the biological level is well represented by the development of the brain. Some 10,000 new brain cells develop per minute during neurogenesis. Many of these cells move to their final location (cell migration). Once there they go through the differentiation process and later in the process, myelination provides an isolating layer around certain axons. Synaptogenesis ensures the formation of synapses. After a period of explosive growth, there is a period of pruning, in which the number of synapses is reduced because little synapses disappear. This makes information processing becoming more efficient. Some brain areas have very specific functions, but for some functions all kinds of brain areas are needed.

Behavioral change mechanisms describe responses to environmental characteristics contributing to development and forming the behavior from the first days of life. An example is habituation: even a fetus can already get used to certain stimuli, but when it is confronted with a new stimulus, we see a reaction (increased heart rate). Habituation motivates babies to seek new stimulation and therefore helps to learn. Classical conditioning also supports learning and generalization ensures that the learned can be applied in other situations. Instrumental conditioning means that behaviors that are rewarded occur more often, while behavior that is punished diminishes. Finally, there is statistical learning, where a child (after only 2 months) learns the likelihood of a particular event following another event. This way the child learns to anticipate the actions of others. Rational learning is related to statistical learning. The previous views are integrated in what actually happens in the environment.

Social learning is learning by observing and interacting with other people. People are much better at this than other species, even when it comes to learning certain skills from other people. Important are imitation, social reference, language and guided participation. Imitation is not just mimicking; when children observe an action failing, they try to find out what the model was trying to do, not what the model actually did. Children also look at the mother's reaction to a situation to determine how they should act in this situation. Another form of social learning is social scaffolding, in which a person with the knowledge of the action gives guidance in the course of the task. As the pupil gets better, he gets more and more responsibility until he can perform the entire task alone.

Four information processing mechanisms are particularly general and omnipresent: basic processes, strategies, metacognition and substantive knowledge. Basic processes include associating certain events with each other, recognizing objects as familiar and retrieving certain facts and procedures. With age, the speed and efficiency of these processes increases. Strategies are used to achieve all kinds of goals, both in the cognitive field and in certain actions and social situations. Metacognition contributes to a greater development, as an increase in the use of memory strategies happens because of an increased realization that large amounts of material cannot be memorized without a strategy. Substantive knowledge means that the more a child knows about a certain subject, the easier it is for that child to include new information on that subject. Children can form connections between new and existing information.

Evolution seems to have provided us with specialized learning mechanisms that enable us to quickly and efficiently learn certain skills that are important for survival. For example, children already know that large moving objects will have a greater impact than smaller moving objects. Informal theories that children have about different types of entities facilitate the learning process. Basic knowledge about certain concepts helps children to act appropriately in new situations.

It is important to remember that all these change mechanisms work together to cause change, even though it is sometimes too easy to examine the different mechanisms separately.

Theme 5: The socio-cultural context forms development

Children develop within a certain context including other people: family, friends, neighbors, teachers and classmates. The context also contains historical, economic, technological and political influences, with social convictions, attitudes and values. What is 'normal' often differs per society and even things that appear to be completely biologically often differ per culture. For example, attachment is influenced by culture: in Japan dependence is welcome, while in the USA independence is preferred. This ensures strongly different attachment styles in children. Some parenting styles that often cause negative outcomes for the child in the US do not have these consequences in other cultures at all. This is probably due to the culturally directed interpretation by the child.

Although over the years the lives of children have improved more and more in the area of health, nutrition, shelter, etc., not all changes have a positive effect on their welfare. Nowadays, children more frequently grow up with divorced parents, resulting in a greater chance of depression, lower self-esteem and worse social skills. More children go to childcare, this does not necessarily have negative or positive effects. Technological changes can have both positive (communication with friends) and negative (cyberbullying) effects. 

Among children who grow up in the same time and society, differences in economic circumstances, family ties and groups of friends can lead to big differences between the lives of these children. Children from poor families perform worse at school, show more insecure attachment styles, experiences more loneliness and run a greater risk of drug use, crime and depression. The cumulative effect of all these factors is the greatest threat to development. Friends and family also have a major influence on development: friendships can provide support but can also carry children into reckless and aggressive behavior.

Theme 6: Individual differences

Children differ on wide variety of dimensions. But, how do we know which are the crucial differences for understanding children and predicting their future? For this, the number of related characteristics, stability over time and predictive value are of great importance. If we take IQ as an example, a high IQ often indicates a better score in other areas (width of related characteristics), that the child will later also have a high IQ (stability over time) and that the high IQ now is predicting positive outcomes in the future (predictive value).   

For a number of important characteristics - including IQ, prosocial behavior and empathy - about 50% of the differences are explained by differences in genetic makeup. This percentage increases as the development continues. Individual differences reflect the experiences of a child in addition to the genes. An important influence comes from the parents. The more stimulating and supportive the home situation is, the better is the intellectual and social development of the child. The best parenting style depends on the characteristics of the child.   

Theme 7: Development research can improve the lives of children

There are a number of points of interest for good parenting:

• Choose a good partner, someone whose physical, intellectual and emotional characteristics suggest that he or she will be a good parent. 
• Ensure a healthy pregnancy: pay attention to diet, little stress, and so on. 
• Know which decisions are likely to affect the long term: take care, for example, that the baby sleeps on his back to prevent child death. 
• Form a secure attachment.
• Provide a stimulating environment, which has a positive effect on learning. 

Also, within education there are points important in improving the development of the child:

• Information processing theories state that analyzing information types in everyday activities can improve learning among children.  
• Sociocultural theories emphasize the value of classifying school classes as learning communities, where the teacher gives a minimal amount of guidance. This ensures that the children learn to use their own competences and the resources of the group.
• When children are at risk of developmental problems, it is important to start the right interventions on time. Timing is that important, because learning problems must be addressed before the child loses his self-confidence and resentment towards the teacher and the school.  
• Also, of importance is early detection of child abuse. There is a higher risk when parents have little money and friends, use alcohol and illegal drugs and when they are mistreated by their partner. It is important that teachers can recognize the warning signals.
• It is impossible to determine the cause of a particular problem, because all problems have a large number of causes contributing to it. In order to be able to give effective treatment, many various difficulties have to be tackled. 

Political decisions also have a major impact on the quality of children's development, particularly with regard to the school system. There is no end to social problems, understanding the development of children can help to focus on the problems affecting the future of children.