Intelligence Testing: Past, Present, and Future

Intelligence testing has long played a central role in education, psychology, and public policy, yet its origins and applications are far more complex—and controversial—than many realize.

First developed in the early 20th century to help identify children needing extra academic support, IQ tests soon became tools for sorting, labeling, and even excluding individuals. From their misuse in the eugenics movement to their widespread commercialization, intelligence tests have shaped perceptions of human ability in ways that often ignore the rich complexity of cognition. Understanding the history and limitations of these tests is essential for making informed decisions in the present and future.

Table of contents:

• Where does intelligence testing come from?
• What is an IQ score?
• What are IQ percentiles?
• So, what exactly is intelligence?
• Does an IQ score predict academic achievement?
• Do IQ scores correlate with job performance?
• What does “multiple intelligences” mean? 
• How reliable are IQ tests?
• What is the Flynn effect?
• So, an IQ score is not fixed, right?
• What does the future hold for intelligence testing?

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Where does intelligence testing come from?

Origins: Intelligence testing began in 1904 when French psychologist Alfred Binet was tasked with identifying children needing special educational support. He and Théophile Simon developed the Simon-Binet Scale, assessing children’s mental capabilities through various tasks. Binet introduced the concept of “mental age,” which led to the creation of the Intelligence Quotient (IQ). However, Binet warned against using IQ as a fixed measure of intelligence, emphasizing that it should guide instruction—not label or limit a child’s potential.

Misuse in the U.S.: Despite Binet’s cautions, American psychologists misapplied his test. H. H. Goddard translated the scale and promoted the idea that intelligence was innate and unchangeable. He classified individuals as “idiots,” “imbeciles,” or “morons” and advocated using IQ scores to sort and control populations. Lewis Terman expanded the test into the Stanford-Binet, which became the dominant IQ test in the U.S., embedding intelligence testing deeply into the educational system.

Eugenics movement: Goddard and others tied intelligence testing to the eugenics movement, which aimed to “improve” the human race through selective breeding. IQ tests were used to justify restrictive immigration laws, forced sterilization, and the institutionalization of individuals deemed intellectually inferior—often based on culturally biased tests.

Commercialization: By the 1920s, intelligence testing had become profitable, with millions of tests administered annually. Despite early misuse, IQ testing gained scientific status, being listed among the top discoveries of the century. Yet, its history is entangled with racial and cultural prejudice. As Harvard’s Stephen Jay Gould argued, such testing often reinforced social inequality rather than scientific objectivity.

Modern perspective: While IQ tests are still widely used today, there is growing recognition of their limitations. Critics argue that these tests often fail to capture the multifaceted nature of intelligence and may not accurately predict academic or life success.

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What is an IQ score?

Even though intelligence testing has existed for over a century, IQ scores are still widely misunderstood. It’s not uncommon to hear comments like, “How can you say my child isn’t gifted? He got 99 on that test—almost a perfect score!” or “The requirement says ‘97th percentile or higher,’ and Jane scored 97—so that qualifies, right?” These remarks reveal a basic confusion about what IQ scores mean.

IQ stands for intelligence quotient, and it’s meant to represent how a person’s cognitive ability compares to that of others. The average score is set at 100. A score above 100 indicates above-average intelligence, while a score below 100 suggests below-average ability. Although, in theory, IQ scores can vary widely in either direction, they typically range from about 50 to 150 in real-world testing scenarios.

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Below is a graphic representation of the above:

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What are IQ percentiles?

IQ is often reported in percentiles, which are frequently confused with percentage scores—a key source of misunderstanding.

A percentage score is straightforward: it reflects how many questions a child got right out of the total. For example, if a child correctly answers 25 out of 50 questions, their percentage score is 50%. If they answer 40 correctly, the score rises to 80%.

A percentile, however, tells us how a child performs relative to others. It indicates the percentage of test takers who scored the same or lower. So, a child who gets 25 questions right and performs better than 50% of their peers would be at the 50th percentile. However, if the same child gets 40 questions right—an 80% score—but everyone else scores higher, they might fall into a much lower percentile despite the high percentage.

In IQ testing, this distinction is important. Most standardized IQ tests are based on a bell curve, with an average (mean) score of 100 and a standard deviation of 15. An IQ of 100 places a person at the 50th percentile—right in the middle. From there, percentiles shift predictably based on how far a score deviates from the average.

IQ	Percentile
65	01
70	02
75	05
80	09
85	16
90	25
95	37
100	50
105	63
110	75
115	84
120	91
125	95
130	98
135	99

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So, what exactly is intelligence?

Great question! Is it doing well in school? Reading and spelling flawlessly? Or are the following people considered intelligent?

• A doctor who smokes three packs of cigarettes a day?
• A Nobel Prize winner with a chaotic personal life?
• A high-powered executive who climbed the corporate ladder—and landed in the hospital with a heart attack?
• A musical genius like Mozart, who composed masterpieces but was constantly broke and dodging creditors?
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The challenge is that intelligence has never been clearly or universally defined. That leaves us wondering—what are IQ tests really measuring?

While there’s no perfect answer, most psychologists agree on one thing: intelligence is the ability to solve problems, and this ability shows up in two main forms:

• Verbal intelligence involves understanding and solving problems through language. It includes reading, listening, writing, speaking, and thinking with words. From classroom learning to social conversations and emails, language-based reasoning is a big part of daily life.

• Nonverbal intelligence, on the other hand, is about understanding and solving problems without words. It’s the ability to reason using visual cues, spatial awareness, patterns, and hands-on logic—like interpreting a map or assembling a puzzle.

Most IQ tests assess both. They include several verbal subtests that measure vocabulary, comprehension, and verbal reasoning—like understanding analogies or solving word-based problems. Here’s an example of a question that taps into verbal reasoning:

Butcher is to knife as hairdresser is to
a.) scissors
b.) hair
c.) curls
d.) blond.

Answer: a

Performance IQ, also known as nonverbal IQ, is measured through subtests that assess skills beyond language. These include spatial reasoning, attention to detail, and visual-motor coordination. In other words, it looks at how well someone can solve problems using visual and hands-on thinking rather than words.

Here’s an example of a task that taps into nonverbal reasoning:

Answer: d

In most individuals, the full-scale IQ, verbal IQ, and performance IQ scores tend to fall within a similar range, suggesting that verbal and nonverbal skills are fairly balanced. However, when there’s a significant gap between verbal and performance scores, it can signal a potential learning difficulty or cognitive difference. For example, a nonverbal learning disorder (NVLD) is often considered when a child’s verbal IQ is 20 or more points higher than their performance IQ.

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Does an IQ score predict academic achievement?

This assumption has already been questioned and answered many decades ago. Goodson and Hess (1976) critically examined the use of IQ scores as predictors of academic success. While IQ tests are often assumed to measure innate intelligence, the document argues that IQ scores largely reflect learned skills and school-based knowledge. As such, IQ is more of an indicator of past learning than an inherent, unchangeable capacity.

The paper reviewed evidence suggesting IQ scores correlate moderately with academic performance, especially in reading and math. However, it emphasizes that this correlation does not imply causation. Environmental factors—like socioeconomic status, access to quality education, and family background—greatly influence both IQ scores and academic outcomes.

The report also challenged the assumption that low IQ scores justify placing students in special education or limiting their learning opportunities. Instead, it advocates viewing intelligence as dynamic and influenced by experience and instruction.

In conclusion, the report cautions against over-reliance on IQ scores in educational decision-making. It recommends using a broader range of assessments that consider both cognitive and environmental factors, arguing that all children should be provided with enriching educational opportunities regardless of IQ.

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Do IQ scores correlate with job performance?

Over the past century, numerous studies have documented the link between cognitive assessment scores and employee performance. In a chapter advocating the principle that employers should ‘‘select on intelligence,’’ Schmidt and Hunter state (2000):

Intelligence is the major determinant of job performance, and therefore hiring people based on intelligence leads to marked improvements in job performance – improvements that have high economic value to the firm.

According to Byington and Felps (2010), the industrial psychology literature has reached a consensus on the explanation for the strong IQ–job performance relationship: more intelligent individuals (as measured by IQ scores) learn job-relevant knowledge faster and better, resulting in improved job performance.

However, many experts question the idea of a single, general intelligence. Intelligence is a broad concept—some say it includes creativity, curiosity, and persistence, qualities that IQ tests don’t measure well. Take James Watson, co-discoverer of DNA: his IQ is around 115, yet he credits his success to relentless curiosity—not high test scores.

IQ tests offer a limited view of intelligence, often failing to capture many important human abilities. Typically, they assess conventional skills, many developing through formal education. In response to this narrow scope, the “multiple intelligences” theory emerged, challenging the idea of a single, general intelligence and promoting a broader, more inclusive understanding of human potential.

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What does “multiple intelligences” mean? 

The theory of multiple intelligences suggests there are many distinct types of intelligence. This idea first gained ground with L.L. Thurstone, a mathematician who noticed that Thomas Edison, a brilliant inventor, struggled with math. Thurstone concluded that intelligence isn’t one thing but many—someone could excel in one area and not in another. He sought to distinguish between academic and practical, social and nonsocial types of intelligence.

Building on this, psychologist J.P. Guilford developed a model identifying 120 types of intelligence, based on different ways the brain processes information.

But, the most widely known theory comes from Dr. Howard Gardner of Harvard. In 1983, Gardner proposed that people have at least eight different intelligences, each representing a unique way of understanding the world:

• Linguistic – word smart
• Logical-mathematical – logic smart
• Spatial – picture smart
• Bodily-kinesthetic – body smart
• Musical – music smart
• Interpersonal – people smart
• Intrapersonal – self smart
• Naturalist – nature smart

This framework expanded how educators and psychologists understand human potential—beyond test scores alone.

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How reliable are IQ tests? 

Numerous studies have shown that IQ tests are far from foolproof. Scores can vary by as much as 15 points, depending on the test. Factors like stress, anxiety, or unfamiliarity with the testing process can all impact results. Researcher Stephen Jay Gould also highlighted how a tester’s attitude, qualifications, and instructions can unintentionally influence outcomes.

In one striking study, 99 school psychologists scored the same IQ test record—and came up with results ranging from 63 to 117 for the same person. In another study, Ysseldyke and colleagues asked professionals to distinguish between students with learning disabilities (LD) and those who were simply low achievers, using only test scores. The professionals—school psychologists and special-ed teachers—were correct just 50% of the time. Surprisingly, a group of university students with no background in psychology or education performed better, identifying LD students with 75% accuracy.

While intelligence testing can provide useful insights, relying too heavily on IQ scores alone can be misleading—and even harmful. IQ is, at best, a rough indicator of academic ability. It makes little sense to claim that someone with an IQ of 110 is significantly more intelligent than someone with an IQ of 105. Such narrow classifications ignore critical influences like home life, education quality, and community support—factors that IQ tests don’t measure.

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What is the Flynn effect?

IQ scores have steadily increased across generations—a phenomenon known as the Flynn effect, named after researcher James R. Flynn. Since standardized testing became widespread in the 1930s, researchers have observed consistent and significant gains in IQ scores worldwide. To maintain 100 as the average, test creators must regularly revise and re-norm IQ tests.

In the U.S., data from widely used tests like the WISC (Wechsler Intelligence Scale for Children) and WAIS (Wechsler Adult Intelligence Scale) show IQ scores increasing by about 0.30 points per year during the latter half of the 20th century. That adds up to more than a 15-point gain—a pattern also seen in many other countries (Flynn, 2012).

What’s behind this rise? The most likely explanation lies in educational progress. As education became compulsory and more children gained access to secondary, higher, and even preschool education, literacy improved and exposure to abstract reasoning increased—both boosting IQ performance. Studies by researchers like Ceci & Williams (1997) and Fernandez-Ballesteros & Juan-Espinosa (2001) support this link between schooling and cognitive development.

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So, an IQ score is not fixed, right?

Correct. An IQ score is not fixed.

A longitudinal study by Ramsden et al. (2011) challenged the long-held belief that IQ is fixed across the lifespan. Following 33 adolescents over four years, the researchers found that verbal IQ (VIQ) and performance IQ (PIQ) can significantly increase or decrease during the teenage years. These IQ changes were not random; they correlated with structural changes in specific brain regions. Gains in VIQ were associated with increased gray matter in the left motor cortex—linked to speech articulation—while PIQ gains were linked to changes in the anterior cerebellum, a region involved in hand movement.

The study used MRI scans and age-appropriate Wechsler intelligence tests at two time points (ages 12–16 and 15–20). While group averages stayed stable, individual scores shifted by as much as 20 points in either direction. This demonstrates that IQ is not static and can be influenced by brain development during adolescence.

The findings prove brain plasticity and suggest that intelligence, especially in teens, is still developing. Educationally and clinically, this supports the view that early IQ scores should not be seen as definitive or permanent measures of a person’s intellectual capacity.

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What does the future hold for intelligence testing?

Intelligence testing is undergoing a major transformation, shifting from rigid, traditional IQ tests to more dynamic, inclusive methodologies. New trends emphasize emotional and social intelligence alongside cognitive ability, with platforms like Psicosmart leading the charge. These tools incorporate interactive, cloud-based, and AI-driven assessments that adapt in real-time, offering deeper insights into individual potential. AI’s role in analyzing patterns and personalizing tests has enhanced accuracy and efficiency, particularly in recruitment.

Technology has revolutionized test delivery, making assessments more user-friendly, scalable, and job-relevant. The future points toward integrating emotional and social intelligence metrics into hiring, improving workplace cohesion and productivity. However, challenges remain. Cultural bias, lack of accessibility, and standardization issues threaten the fairness of intelligence assessments. Ethical concerns also surface, especially with genetic intelligence testing, which risks reinforcing inequality and reducing complex traits to biological determinism.

In sum, the future of intelligence testing lies in a more holistic, adaptable, and inclusive approach—one that values growth, diversity, and real-world skills over static scores. The challenge is not just to measure intelligence but to do so wisely, fairly, and humanely.

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Edublox offers cognitive training and live online tutoring to students with dyslexia, dysgraphia, dyscalculia, and other learning disabilities. Our students are in the United States, Canada, Australia, and elsewhere. Book a free consultation to discuss your child’s learning needs.

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References:

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Intelligence Testing: Past, Present, and Future was authored by Sue du Plessis (B.A. Hons Psychology; B.D.), an educational specialist with 30+ years of experience in the learning disabilities field.

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