“Intelligence” is in quotes because it is a fraught subject for technical and political reasons, raising issues of its nature, how it is tested, and the uses of results.  This cursory overview is even less reliable than other pages on this site.

Competing definitions History IQ The "Bell Curve"
Components The “g” factor Political issues Multiple Intelligences
Can intelligence be taught? Beliefs about intelligence (mindsets)
Fluid and crystallized intelligence Convergent and divergent thinking

Factors in Educational Achievement

Go here for a fuller account and (now dated) literature review (APA, 1995)

The idea

Intelligence is meant to be a generalised measure of overall ability, or potential ability: its proponents claim that it is getting at an underlying feature which is independent of specific skill development or learning achievement.  


Competing definitions

The problem is that it is difficult to get a consensus about what "intelligence" actually is:

  • "The power of good responses from the point of view of truth or fact" (Thorndike)

  • "A biological mechanism by which the effects of a complexity of stimuli are brought together and given a somewhat unified effect in behavior" (Peterson)
  • "The ability to carry on abstract thinking" (Terman)
  • "The ability to adapt oneself adequately to relatively new situations in life" (Pintner)
  • "The capacity for knowledge, and knowledge possessed" (Henmon)
  • "The capacity to acquire capacity" (Woodrow)

"Viewed narrowly, there seem to be almost as many definitions of intelligence as there were experts asked to define it" (Sternberg 1987)  


  • Francis Galton (1884) — convinced that there must be biological factors underpinning achievement in society—measured head size, reaction time etc., but found no correlations
  • Alfred Binet (1905 on) devised tests to determine ineducability (to meet the requirements of a new French law prescribing schooling for all educable children) and formulated the idea of "Mental Age" from which developed the idea of the "Intelligence Quotient" (see below)
  • Lewis Terman (at Stanford University) adapted and standardised the Binet tests for American children (1916, and routinely revised since) known as the "Stanford-Binet" tests.
  • David Wechsler developed the Wechsler Intelligence Scale in 1939: hitherto tests had been confined to children.

IQ Tests on the Net

Intelligence Quotient (IQ)

IQ =  

Mental Age x 100

Chronological Age

So if the Mental Age = Chronological Age, IQ = 100, the notional average. The distribution of IQ supposedly follows a normal distribution curve (or "Bell Curve"), and assessment of "superiority" and "inferiority" is determined by the number of statistical Standard Deviations above and below the mean.

However, the "Flynn effect" suggests that IQ scores have been rising over time, so that the initial norm of 100 is no longer valid. This is of course problematic because of different approaches to measurement.

The Flynn effect

and more on the Flynn effect

The “Bell Curve


<20 20-34 35-49 50-69 70-89 90-109 110-129 130+
 Profound learning difficulty Severe learning difficulty Moderate learning difficulty Mild learning difficulty Low normal Normal High normal “Genius”

The Bell curve referred to in Herrnstein and Murray's (1995) famous (or notorious) book is simply the normal distribution curve which IQ tests were set up to plot. 68% of the population come within one standard deviation of the mean, and 95% within two standard deviations: that is an artefact of the definition of a statistical "standard deviation".


The fifth edition of the Stanford-Binet Test —one of the accepted standard tests—examines five broad areas of intelligence, which are supposed to be independent of each other, and not culture bound. (The 1986 fourth edition did not include "fluid reasoning")

verbal reasoning

abstract/visual reasoning

quantitative reasoning

working memory

fluid reasoning

However, there is considerable argument as to whether these are simply more specific manifestations of a more general underlying feature, known as the g factor.

Spearman's g Factor

The g (for "general") factor is arrived at by factor analysis of results from tests and is suggested as the main underlying component, supplemented by components relating to more specific aptitudes. Critics suggest g is an artefact of method, since Spearman was a statistician rather than a psychologist, although it is conceded that “intelligence” may have a hierarchical structure.

At the other end of the scale is the notion of multiple intelligences, suggested by Howard Gardner.

Links for scholarly discussion of the g factor: difficult to navigate but worth it

See here for a "pro-g" article

Correlations with Achievement

Clearly, high intelligence may be expected to correlate significantly with educational achievement. The correlation is positive, but declines substantially as students proceed through the system:

 Primary school 0.6-0.7

 Secondary school 0.5-0.6

 College 0.4-0.5

 Post-graduate 0.3-0.4

 Figures from US. terminology revised for UK: from Atkinson et al (1993)

Factors in Educational Achievement

As the correlation figures show, intelligence alone is not sufficient to account for academic achievement: it is certainly necessary, but beyond a certain threshold, it is by no means clear how much.

As education progresses, other factors come into play, such that the limits are determined by the strength of the weakest link in the chain.


Political issues

  • Intelligence has been a fraught political issue, ever since Francis Galton attempted to measure ability to support his eugenic theories. Early abuses in the United States included compulsory sterilisation of people with low IQ (Gould, 1984).
  • In the UK, Sir Cyril Burt's work on IQ was the basis of selection at 11+, in the 1944 Education Act. In the 1970s, Burt was accused of fraudulent results because some of his findings were too significant: he appears to have been rehabilitated, but there are still some unanswered questions.
  • Arthur Jensen (1969) was accused of racism when he suggested that white children were more intelligent than blacks (and that Asian children were brighter than either). Latterly, the controversy has been revived by Herrnstein and Murray (1995) and publication of Chris Brand's book The g Factor was abandoned at the last minute in 1996 because of concerns about his self-confessed "scientific racism"   
  • For critical reviews of these issues see Montagu (1999) and Richardson (2000)

Can intelligence be taught?

There is considerable debate over the hereditary component in intelligence, and the picture is getting more complicated all the time, but at least one school believes that intelligence can largely be identified with "problem-solving skills" or even forms of pattern recognition and that as such it can be taught. (Feuerstein, 1980—see Sharron’s more accessible account— Soden 1994)

On the so-called "nature versus nurture" debate in general see Ridley (2003) for a brilliant and accessible exposition of how far science has moved beyond the question.

Frankly, the idea is so slippery that this question can never be answered (unless neuroscience changes the game radically); but what people believe about the answer—especially in relation to themselves—can make a great difference to how they face challenges and difficulties. See Intelligence and Self-theories.


What does this mean in practical terms for teachers?

The construct of "intelligence" was the most potent psychological notion affecting educational policy in the last century. In 1958, in "The Rise of the Meritocracy, 1870-2033" Michael Young envisaged a world in which intelligence was the sole determinant of status in society: re-reading it today it sometimes seems quaint, but sometimes uncannily accurate and trenchant.

In practice, the label has been used mainly for labelling, whether the unforgiving watershed of the 11+ exam in the UK, until the introduction of the comprehensive system, or more currently the application of "Atherton's law": "The amount of attention paid to teaching and learning is in inverse proportion to the perceived ability of the students." The discourse of "bright" versus "thick" or "stupid" still pervades the informal and unaccountable judgements of teachers on students. It remains their traditional exculpatory angle. But apart from that, what can you do with it?

For some people, it has been a life- (or at least career-) saver: the discrepancy between this measure of potential and those of achievement has shown that they were severely under-estimated. Einstein is the classic case, but IQ was not an idea in use in his ignominious early career. On the other hand, its record as a self-fulfilling prophecy outweighs this: the Rosenthal and Jacobson study epitomises the issue.

1968 article by R and J summarising the research; requires access permission. Simple but reliable account of the experiment here

(For the record: at age 14, my score on the full Stanford-Binet battery was supposedly 158—but only because I was able to persuade the tester (a gullible rookie clinical psychologist) that some of my answers were just as valid as the standard ones. If he had been any good, he would never have betrayed by his expression that some of them were "wrong"! I've been suspicious ever since. On the other hand, the ability to persuade the tester that your unorthodox answers are legitimate may be a valid indicator of "intelligence"...)

Sternberg R (1987) "Intelligence" in R L Gregory (ed) The Oxford Companion to the Mind Oxford; OUP, 1987 [Back]

up-dated 15.01.11

To reference this page copy and paste the text below:

Atherton J S (2013) Learning and Teaching; [On-line: UK] retrieved from

Original material by James Atherton: last up-dated overall 10 February 2013

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