How The Scale Was Derived

The tests were arranged in order of difficulty, as found by trying them upon some

200 normal children of different ages from 3 to 15 years. It was found, for illustration,

that a certain test was passed by only a very small proportion of the younger

children, say the 5-year-olds, and that the number passing this test

increased rapidly in the succeeding years until by the age of 7 or

8 years, let us say, practically all the childr n were successful.

If, in our supposed case, the test was passed by about two thirds to

three fourths of the normal children aged 7 years, it was considered by

Binet a test of 7-year intelligence. In like manner, a test passed by

65 to 75 per cent of the normal 9-year-olds was considered a test of

9-year intelligence, and so on. By trying out many different tests in

this way it was possible to secure five tests to represent each age from

3 to 10 years (excepting age 4, which has only four tests), five for

age 12, five for 15, and five for adults, making 54 tests in all.