Alfred Binet, answered from the texts and cited to the page.
Mental level is, at its core, a position on a scale — a classification of where a given child's intelligence stands relative to the normal development of children of the same age. The scale itself is a series of tests of increasing difficulty, beginning from the lowest intellectual level that can be observed and rising to that of average normal intelligence, with each group in the series corresponding to a different mental level.1
I must be precise about what this means and what it does not mean. The scale does not permit the measure of intelligence in the strict sense, because intellectual qualities are not superposable — they cannot be laid alongside one another and compared as one compares linear surfaces — but it does permit a classification, a hierarchy among diverse intelligences, and for the necessities of practice this classification is equivalent to a measure.2
From it we can determine how many years a given child is advanced or retarded relative to the normal course of development. In practice, a child's mental level is fixed by the highest age at which he passes all the tests, with the allowance of one failure; and beyond that, a compensating rule gives him the benefit of an additional year for every five tests he passes above his fixed level.3
The procedure is, I freely admit, partly conventional — adopt a different rule and you arrive at somewhat different results — and one must remember that the expressions "retarded" or "advanced intelligence" carry this artificial character with them.4 They describe a present state, not an eternal verdict. That last point is the one I press most firmly.
Our purpose in measuring the intellectual level of a child brought to us is to study his condition at the time and that only — we set aside etiology, we set aside prognosis, we limit ourselves to ascertaining the truth in regard to his present mental state.5 The mental level is a diagnostic finding, not a sentence on the child's future. It tells us where to begin helping him; it does not tell us that help is useless.
This scale is composed of a series of tests of increasing difficulty, starting from the lowest intellectual level that can be observed, and ending with that of average normal intelligence. Each group in the series corresponds to a different mental level.The Development of Intelligence in Children
This scale properly speaking does not permit the measure of the intelligence, because intellectual qualities are not superposable, and therefore cannot be measured as linear surfaces are measured, but are on the contrary, a classification, a hierarchy among diverse intelligences; and for the necessities of practice this classification is equivalent to a measure.The Development of Intelligence in Children
A subject has the intellectual development of the highest age at which he passes all the tests, with the allowance of one failure in the tests for that age... give him the benefit of an advance of one year every time he passes at least five of the tests beyond his level.The Development of Intelligence in Children
These expressions, because they are arbitrary, might cause some illusions. It is necessary to remember that the expression 'retarded' or 'advanced intelligence,' results partly from the conventional procedure that we have adopted.The Development of Intelligence in Children
Our purpose is to be able to measure the intellectual capacity of a child who is brought to us in order to know whether he is normal or retarded. We should therefore, study his condition at the time and that only... We shall limit ourselves to ascertaining the truth in regard to his present mental state.The Development of Intelligence in Children