"Development is a complex process of growth and change.. through which children acquire a variety of skills and abilities that allow them to understand and function in their world (Gioia, 1993, p.52)."
How well, or how quickly a child develops is dependent on two key factors:
1) Nature- the genetic characteristics present from birth, which includes the inborn potential to learn.
2) Nuture- the experiences and environments that influence inborn potential and determine how it will be expressed.
While our genetic predisposition (nature) pre-sets a limit on development, it is our environment and our experiences (nuture) which can contribute to, or detract from our developmental outcome, based upon their quality!
Even with 'equal' genetic predispositions, two similar individuals can have very different outcomes, depending on the quality of their experiences and their environment.
An adequately enriching and stimulating environment can assist the child to develop to their maximum potential. An environment which is deficient or inadequate socially, emotionally, or in stimulation of abilities can prevent the child from achieving an outcome appropriate to his or her inborn potential.
This fact continues to motivate us to identify the kinds of experiences, environments, interventions, educational strategies, etc., that are most conducive to enhancing development!!

What is Normal Development?

From one child to the next, there can be great variability, or differences, in development. However, "...there are earlier and later limits to what is considered 'normal development' (Gioia, 1993, p.66)."
Normal development is characterized by the achievement of certain skill "milestones" by a certain age, or within a certain age range. Gioia (1993) outlines some of the typical age ranges for a number of developmental milestones.
A normally developing child will reach for and handle objects by the age of about 6 months, and at about the same age will be able to sit without support. Anytime between the ages of nine to 14 months, the normally developing child will take their first independent stepsj.
Between the ages of one and two years, the normally developing child will say their first word. At the age of three the normally developing child is able to take turns and to cooperate with 2-3 other children in play activities.
At age four the child can use 4-7 word sentences and to describe their own experiences. By the age of five, the normally developing child will be able to tie his or her shoe-laces and is able to think through and solve problems.

What is Abormal Development?

While most children (68% approximately) will demonstrate certain skills within certain (normal) age parameters, there are others who will manifest delays in demonstrating these skills (about 16%) and there are others who will demonstrate these skills in advance of "the norm". (another 16% of all children)
Of these 32% of children who either fall below or above "the norm", about 2 1/2 percent will show SIGNIFICANT delays or even absence of the development of some skills, while another 2 1/2 percent will demonstrate SIGNIFICANT early development of these skills.
In later life, the 2 1/2 percent of the children falling significantly below the norm, may receive a diagnosis of "mental retardation"; those 2 1/2 percent falling significantly above the norm may later be identified as "gifted".

Terminology: Mental Retardation or Developmental Disability?

A developmental disabiltiy is a condition that appears early in life and has a life-long effect on the way an individual grows and acquires skills, or develops.
By this definition, the term "developmental disabiltiy" can refer to any number of life-long conditions. In fact, in clinical literature (e.g. medical and professional journals, textbooks etc.) and in American legislation, the term "developmental disability" is used to refer to ANY disability which negatively impacts on development. That includes "mental retardation", as well as epilepsy, cerebral palsy, autism, neurological disorders, etc.
Here in Ontario, however, when we use the term "Developmental Disability", we are refering specifically and only to the developmental disorder of "Mental Retardation". In fact, the term "Mental Retardation" is actively rejected by most community agencies, advocacy organizations, and the labeled persons themselves.
While the term "Mental Retardation" is still an accepted medical and clinical term and a "proper" diagnostic label, it is considered by community agencies to be outdated, stigmatizing, negative and archaic.
We will be using the term "Mental Retardation" interchangeably with the term "Developmental Disability". This will often be presented as MR/DD. (Mental Retardation/Developmental Disability)
We will be sensitive, however, to the positions and philosophies of the community agencies who serve persons affected by "Mental Retardation" and make every effort to avoid using that term in community settings where it is considered to be unacceptable by the agencies and/or by their consumers.

Developmental Disability or Developmental Dilay?

Often you will hear people use the terms "developmental disability" and "developmental delay" as if they meant the same thing. They are, however, different.
A developmental delay means the child is behind where he should be for his age in one or more areas of learning. The word 'delay' implies that the child may yet 'catch up' to his peers at some point.
The label of developmental delay is often given as a tentative diagnosis to infants and young children when the reasons for the delay are not known and/or there is uncertainty as to the "permanence" of the delay.
Ther term "developmental disabiltiy" refers to a permanent condition. The individual is not expected to ever 'catch up' to his age peers.
A developmental disability might be diagnosed at a very early age (particularly if the child has a recognizable syndrome of MR/DD, such as Down Syndrome), or it might be given after a period of time during which the 'delayed' child fails to show improvement in their development to the extent that they begin to approach the norm for their age peers.
Therefore, we will use ther term "developmental delayed" when we speak about infants or young children who are not developing within the normal range, and for whom a definitive diagnosis of a syndrome of MR/DD had not yet been established. However, we will use the term "developmental disabled" (and never the term "developmental delayed") when we speak about youth (12-18 yrs) and adults who's achievements differ significantly from their age peers.