All the individuals differ in mental traits is much as they do in physical features. Whatever the conception of intelligence, all the psychologists and educators and even common people have believed since ancient times that there are various levels of intelligence some individuals are more intelligent than the others.
We come across some men who are giant intellects and at the same time there are some unfortunate people who are devoid of intelligence and cannot count up to ten even after full maturity. Between the genius and the idiot there lie all grades of intelligence both above average and below average.
With the advent of the 20th century there appeared a ray of hope in this connection. The educational authorities of Paris were very much disgusted with the leakage of students in Primary Schools due to their backwardness in studies. They wanted to know the basic causes of the backwardness.
The problem was entrusted to Alfred Binet, renowned medical practitioner interested in psychology. Alfred Binet worked on this hypothesis that children fail in studies due to poor intelligence.
Now he wished to ascertain if the intelligence of such children who had left school was really very low and that of those students who were doing well in schools was quite up to the mark.
There was no objective instrument of measurement of intelligence so far. There arose the need of some reliable objective tests. He endeavored to create the same in collaboration with Simon.
Both the psychologists prepared the first objective test of Intelligence in 1911. After laborious experiments and thorough research, Binet reached the conclusion that no single performance could measure this faculty adequately.
Therefore, he included many small problems concerning various situations in his test. He soon discovered that intelligence develops gradually with age. Therefore, many tests suitable for many grades of children according to their agewere constructed. They were tried on large samples and were standardized for various age levels.
Binet and Simon discovered that all children could not attempt the test standardized for their particular age level although a large number out of the same could do the same. For example, a nine-year old should be able to do the test standardized for his age group.
But sometimes a child could not do well in it. He was then offered the test for lower age groups. Suppose he succeeded in a doing well in the test prescribed for the seven year age group.
Then his mental age was declared to be seven years although his chronological age was nine years (chronological age is the actual age of the individual counted in days, months and years from the day of his birth). Similarly, a child of nine years could have mental age of nine, ten, eleven or more years.
All such individuals whose chronological age corresponded with their mental age were thought, to be normal or average in intelligence. All the individuals whose mental age was more than their chronological age were declared to be of superior intelligence while individuals with fewer mental ages were believed to be below normal in intelligence.
Terman gave a new concept of Intelligence Quotient to the world. Binet gave the mental age along with the chronological age of the individual. One could know the intelligence level of child by comparison of both the ages.
Terman went a step further. He multiplied the mental age with one hundred and divided the result by she chronological age. It gave intelligence Quotient (I.Q.).