A below-average IQ is any score under 85 on a standardized intelligence test. The average IQ is set at 100, with a standard deviation of 15 points, so a score of 85 falls exactly one standard deviation below the mean. About 16% of the population scores below this threshold, and only 2.2% scores below 70, which is the range associated with intellectual disability.
How IQ Scores Are Distributed
IQ scores follow a bell curve, with most people clustered near the middle. Roughly 82% of the population falls between 85 and 115, the range considered average. Scores between 70 and 85 are often described as “low average” or “borderline,” while scores below 70 fall into the range where intellectual disability may be diagnosed, though a diagnosis also requires difficulties with everyday adaptive skills like managing money, holding a job, or living independently.
These categories aren’t rigid cutoffs. The American Psychiatric Association notes that clinicians shouldn’t be rigidly bound to the 65 to 75 IQ range when evaluating intellectual disability. Someone scoring 75 with strong real-world coping skills is in a very different situation than someone scoring 75 who struggles to navigate daily life.
What Scores Between 70 and 85 Look Like in Practice
The 70 to 85 range, sometimes called borderline intellectual functioning, is a gray zone. People in this range don’t qualify for most disability services, yet they face measurable challenges. Research published in the European Journal of Investigation in Health, Psychology and Education found that individuals in this range have notably lower employment rates, tend to work in low-skilled and precarious jobs, and struggle with the organizational skills and training that employment demands. When they do find work, workplace marginalization and underemployment are common.
Independent living presents its own obstacles. Household management, financial skills, money management, and administrative tasks are areas of particular difficulty. Social judgment, the ability to read situations and make sound decisions in real time, is often impaired, which compounds challenges in both work and daily life. Many people in this range need some degree of external support to achieve full independence, even though they wouldn’t meet criteria for an intellectual disability diagnosis.
This gap in support is a well-documented problem. Because these individuals fall above the threshold for most services, they often go without the help that could make a significant difference in their quality of life.
What Shapes IQ Scores
IQ is influenced by a mix of genetics and environment, and the environmental factors matter more than many people realize. Lead exposure is one of the most studied contributors to lower cognitive scores. Prenatal exposure to lead, even at levels once considered safe (below 10 micrograms per deciliter of blood), can have lasting negative effects on a child’s cognitive development. Old paint in buildings and contaminated soil near busy roads or factories remain common sources of exposure.
Other environmental toxins, including certain industrial chemicals, have similar effects. One encouraging finding: in children prenatally exposed to PCBs (a class of industrial pollutant), breastfeeding appeared to offset the cognitive damage, likely due to the beneficial nutrients in breast milk. Nutrition, access to early education, household stability, and exposure to language all play roles in how cognitive ability develops during childhood.
How Stable Are IQ Scores Over Time
By middle childhood, IQ scores become remarkably consistent. Research published in the Proceedings of the National Academy of Sciences found that scores measured between ages 8 and 10 correlate strongly with scores taken 10 to 20 years later. That stability persists deep into old age: one study found a strong correlation between IQ measured at age 11 and IQ measured at age 90.
This doesn’t mean IQ is completely fixed. Scores can shift by several points in either direction, particularly in response to major changes in environment, education, or health. But for most people, a score in the low-average range during childhood tends to remain in roughly that range through adulthood. Early interventions, particularly in nutrition and education, have the best chance of producing meaningful shifts.
IQ Tests Have Real Limitations
A below-average score doesn’t always reflect a person’s true cognitive ability. Standardized IQ tests were originally developed using small, culturally narrow samples (the first widely used test was normed on just 200 children in France), and decades of research show persistent score gaps between racial, ethnic, and socioeconomic groups. Black and Hispanic students, immigrants, and non-native English speakers consistently score lower on these tests, not necessarily because of differences in ability but because the tests measure skills and knowledge shaped by cultural context.
Cognitive skills develop differently depending on the environment a person grows up in. Someone raised in a community where problem-solving looks different from what a Western-designed test expects may score poorly despite being highly capable. Motivation also plays a role. A meta-analysis found that accommodations designed to improve motivation during testing significantly boosted performance among examinees with below-average IQ, suggesting that some low scores partly reflect disengagement rather than low ability.
Health and Longevity Connections
Large population studies have found that people with higher childhood IQ scores tend to live somewhat longer than those with lower scores. A landmark study tracking every child born in Scotland in 1936 from age 11 through age 79 found that higher IQ was associated with lower rates of death from heart disease, stroke, cancer, respiratory disease, and dementia. The relationship followed a dose-response pattern: the lower the score, the higher the risk, with the clearest gradients for cardiovascular disease and smoking-related cancers.
The reasons are complex. People with higher IQ scores tend to end up in safer occupations, are less likely to smoke, and may be better equipped to navigate healthcare systems. But even after researchers adjusted for smoking status and occupational class, significant associations between childhood IQ and mortality remained, suggesting that cognitive ability influences health through pathways beyond just behavior and socioeconomic status.
Support in School Settings
Students who score in the low-average or borderline range often benefit from classroom accommodations, even when they don’t qualify for special education services. Under Section 504 of the Rehabilitation Act, students with cognitive challenges can receive legal protections and adjustments to how they’re taught and assessed.
Practical strategies that help include simplified instructions that emphasize key phrases, extended time to respond to questions, frequent breaks to account for shorter attention spans, and testing in familiar environments. Visual cues for behavioral expectations and breaking tasks into smaller steps also make a meaningful difference. These aren’t about lowering standards. They’re about giving the student a fair chance to demonstrate what they actually know.