A theory of development is a scheme or system of ideas that is based on evidence and attempts to explain, describe and predict behaviour and development. Motor development relates to the development of motor skills and consists of motor milestones, the basic motor skills acquired in infancy and early childhood (e.g: sitting, crawling). Motor development gives an individual the ability to act on the world.

The maturational theories by Gesell state that motor development proceeds from the global to the specific in two directions:

1. Cephalocaudal trend
   This is development that proceeds from head to foot along the lengths of the body. The head is controlled first here.
2. Proximodistal trend
   The development of motor control in infancy which is from the centre of the body outwards to more peripheral segments. The centre of the body is controlled first here.

This theory states that maturation alone shapes motor development. Development is controlled by a maturational timetable linked to the central nervous system and to muscular development. This theory does not account for considerable individual differences in the acquisition of various motor skills.

The dynamic systems theory views the individual as interacting dynamically in a complex system in which all parts interact. This theory states that all new motor development is the result of a dynamic and continual interaction of three major factors, the nervous system development, the capabilities and biomechanics of the body and environmental constraints and support.

A study on infant kicking showed that infants are able to change their pattern of interlimb coordination. A study on infant reaching showed that before infants start to reach they will stabilize their heads because this gives the infants a base to reach from. This shows that motor skills are learned through a process of modifying and developing their already existing abilities. A study on infant walking showed that infants do not have a fixed and rigid understanding of their own abilities and have the dynamic flexibility to adjust their abilities as they approach each novel motor problem.

Piaget stated that children are active agents in shaping their own development and that they learn to adapt to their environment as a result of their cognitive adaptations. There are two important processes necessary in order to adapt to the world:

1. Assimilation
   This is the process through which children incorporate new experiences in their pre-existing schemes. It is what happens when we treat new objects, people and events as if they were familiar.
2. Accommodation
   This is the process through which children adapt to their new experiences by modifying their pre-existing schemes.

These processes are functional invariants, processes that do not change during development. Cognitive structures (schemas) do change. According to Piaget, there are four broad stages of development:

1. Sensorimotor stage (birth to 2 years)
   In this stage, thought is based primarily on perception and action and internalised thinking is largely absent. Thinking is doing in this phase and object permanence is learned.
2. Preoperational stage (2 to 7 years)
   In this stage, children are unable to coordinate aspects of problems in order to solve them. They are egocentric and tend to show animism, the idea that moving things are alive. Children in this stage lack the logical framework for thought. Children in this stage also show centration, the focusing or centring of attention on one aspect of a situation to the exclusion of others (e.g: only looking at the increase of length and not the increase of width).
3. Concrete operations stage (7 to 11 years)
   In this stage, reasoning becomes more logical, systematic and rational in its applications to concrete objects. Children in this stage are able to pass the conservation task.
4. Formal operations stage (11 years to later)
   In this stage, the individual acquires the capacity for abstract scientific thought. This includes the ability to theorise about impossible events and items.

Information processing approaches view the human mind as a complex system through which information flows. This approach holds the view that cognitive processes are explained in terms of inputs and outputs and that the human mind can be compared to a computer, this comparison makes use of connectionist models. Connectionist models are computer programs designed to emulate some aspect of human cognition.  This view is a bottom-up view. Constructivism is the theoretical view that infants are not born with knowledge but instead gradually construct knowledge. They construct their own cognition.

Infants may have limits on knowledge acquisition because of relatively immature perception. Infants learn to perceive causality between 4 and 6 months. Young infants are also unable to perceive object unity, although they learn this relatively quick. Children use different strategies in trying to solve problems and hone their choices with experience.

The development of intellectual abilities is influenced by a relationship with more advanced individuals according to Vygotsky. He stated that language is external before it is internal and that the social environment is the most important factor in development. The zone of proximal development is the zone in which a child can solve problems with the help of a more advanced individual and can thus develop. If a problem is beneath this zone, the individual can solve the problem without any help and if the problem is above the zone, then the individual cannot solve the problem, even with help.

Pavlov stated that individuals learn an association between two stimuli because of the timing of the presence of the stimuli. The law of effect states that the likelihood of an action being repeated is increased if it leads to a pleasant outcome and decreased if it leads to an unpleasant outcome. Operant conditioning is a form of conditioning which uses reinforcement and punishment. The social learning theory of Bandura emphasises the importance of observational learning. Bandura argued that children can imitate the actions of others, based on perceived reinforcement. The social cognitive theory emphasises social factors in cognitive development.

The most important unit in evolution is the gene. Chromosomes are strands of DNA and are made up of genes. Ethological approaches are approaches which emphasise the evolutionary origins of many behaviours that are important for survival. There are two implications of ethology’s conception of behaviours. They require an external stimulus or target (e.g: imprinting requires a target) and there is a critical period in which the young have to be exposed to a particular skill or experience in order for it to be learned.

Bowlby argued that attachment was a primary drive, instead of a secondary drive, as was argued by behaviourists. Evidence from this comes from experiments with rhesus-monkeys by Harlow. These experiments showed that the cloth monkeys provided contact comfort. Monotropy is the view that the infant has a basic need to form an attachment with one significant person. Monotropy is also shown in the strange situation test.

Freud claimed that much of the behaviour is determined by unconscious forces of which we are not directly aware. He suggested that there are three main structures to personality:

1. Id
   This is a primitive collection of urges with which an individual begins life.
2. Ego
   This is rational thought that controls the urges of the id.
3. Superego
   This is a collection of ideals, morality.

According to Freud, there are five psychosexual stages through which a child develops:

1. Oral stage (birth to 1 year)
   The greatest satisfaction is derived from the oral areas of the body.
2. Anal stage (1 to 3 years)
   The greatest psychosexual pleasure is derived from the anus.
3. Phallic stage (3 to 6 years)
   This is the time when children obtain their greatest pleasure from stimulating the genitals. At this time, boys experience the Oedipus complex and girls experience the Electra complex.
4. Latency and genital stages (6 years to adolescence)
   The child’s sexual awakening goes into a resting period latency and at adolescence sexual feelings become more apparent and urgent and the genital stage appears.

The main problem with the Freudian theory is that much of what motivates us is determined unconsciously. Besides that, it is almost impossible to test.

Humanistic theories focus on the individual’s own subjective experiences, motives and desires. There is an inner desire for self-actualisation and people free will is a central point in humanistic theories. Maslow suggested that there is a hierarchy of needs. One stage has to be fulfilled before the other stage can be fulfilled.

Gender development is the developing understanding by a child that it is either a girl or a boy and that there are gender-appropriate behaviours associated with this difference. Gender constancy is the awareness, in early childhood, that one is either a boy or a girl and that this is unchangeable. Bandura states that a child is reinforced for showing gender-appropriate behaviour. According to the psychoanalytic view, gender develops from the resolution of the complexes. Prenatal and early-infantile hormones have a strong influence on gender development and other gender dimorphism characteristics.

There are three main issues in child development;

1. Nature-nurture issue
   This is the debate on whether development is the result of an individual’s genes or the kinds of experiences they have throughout life.
2. Stability versus change
   This is the question of whether individuals are stable in the sense of maintaining their rank order across age. The question is whether things such as shyness in young children are stable during development and if early experiences shape later life. It turns out that some things are unstable and some things are stable.