As the child grows, there is no doubt that the age IQ becomes stable. It then brings us to the question of what is IQ? An intelligence quotient is a total score derived from a set of standardized tests or subtests designed to assess human intelligence. IQ scores have been shown to be associated with such factors as nutrition, parental socioeconomic status, morbidity and mortality, parental social status, and perinatal environment.
Three assessments of intellectual performance at each of four developmental periods served as indicators of latent intelligence during infancy (1, 1.5, and 2 years old), preschool (2.5, 3, and 3.5 years old), childhood (6, 7, and 8 years old), and adolescence (12, 15, and 17 years old). Intelligence exhibited a high degree of stability across the four developmental periods. Further, from infancy to adolescence, the effect of intelligence during earlier periods was completely mediated by intelligence during the adjacent developmental period.
The age at which intelligence quotient, or IQ, becomes stable marks a significant stage in human cognitive development. In early childhood, intellectual abilities tend to change rapidly as the brain grows and adapts to new experiences, learning opportunities, and environmental influences. During this period, children’s thinking, reasoning, and problem-solving skills develop quickly, making their IQ scores more variable. However, as individuals reach later childhood and adolescence, the brain’s structure and cognitive functions begin to mature, leading to greater consistency in intellectual performance.
Researchers generally agree that IQ becomes relatively stable around the age of adolescence, when most of the major developmental changes in the brain have taken place. From this point onward, while learning and knowledge can continue to expand, a person’s general level of cognitive ability remains fairly constant over time. This stability reflects the balance between inherited intelligence and environmental experiences that shape mental growth, helping psychologists better understand how intelligence develops and persists throughout life.
Contents
IQ Stability Age
From 6 years old onward, correlations among IQ scores range from moderately strong to strong, suggesting that IQ scores are relatively stable once children reach school age.
Correlations among IQ scores increase as children advance in age with correlations between IQ scores measured 3 years apart. Correlations increased from 0.32 (between IQ scores at 2 and 5 years old) to 0.70 (between IQ scores at 5 and 8 years old), and then to 0.85 (between IQ scores at 9 and 12 years old).
Results also showed a slight tendency for correlations between IQ scores to increase with age. The correlation between IQ scores at 3 and 6 years old was 0.73, the correlation between IQ scores at 5 and 8 years old was 0.79, and the correlation between IQ scores at 9 and 12 years old was 0.81.
Again, the strength of correlations between IQ scores may also be a function of the length of the measured interval. Therefore, to evaluate whether the relations between IQ scores increase with age, it is essential to define a uniform measured time interval.
Only a few studies have investigated the stability of IQ scores from infancy through adolescence because of the challenge to recruit infant participants and then track and assess their intellectual development for over 15 years.
Generally, it’s widely accepted that IQ stabilizes around the age of 6 or 7. Before then, the brain is in a plastic enough state that IQ can actually be increased up to 1 standard deviation but past that age, your IQ, and therefore general intelligence, is relatively stable.
Age by Age: IQ Improvement Clues in Children
IQ improvement in children happens through different stages of cognitive development as they grow. From birth to around age two, children learn primarily through their senses and actions, gradually building understanding of the world like realizing that objects exist even when out of sight, which lays the groundwork for future learning. Between ages two and seven, language skills and symbolic thinking improve rapidly, although children’s thinking is still quite concrete and egocentric, meaning they struggle to see things from others’ perspectives.
As children move from about seven to eleven years old, their reasoning becomes more logical and organized; they understand concepts such as quantity conservation and begin to consider other people’s thoughts and feelings more clearly. From around twelve years onward, during adolescence, children develop the ability to think abstractly, reason scientifically, and solve complex hypothetical problems, which greatly enhances their overall intellectual capabilities.
These stages are influenced by genetic growth, environmental stimulation, social interactions, and educational experiences, all of which contribute to the gradual improvement of IQ and cognitive skills at each age range.
The clues to IQ change significantly from infancy to toddlerhood, reflecting the development and refinement of core cognitive abilities. In infancy, IQ clues are seen primarily through basic cognitive processes such as attention span, processing speed, memory capacity, and representational competence, the ability to mentally represent objects and events.
IQ tends to become relatively stable around the age of 10. While children’s cognitive abilities can develop rapidly in the early years, there’s a lot of variation due to growth, environment, and learning experiences. By the time a child reaches late childhood—usually between ages 8 and 10—their IQ scores start to show more consistency over time. From this point forward, while life experiences, education, and environment can still influence how a person uses their intelligence, the core level of cognitive ability measured by IQ tests tends to remain stable through adolescence and into adulthood. This is how it works:
-
Ages 0-2
Read to your child. Often. Talk to him, using direct and sustained eye contact. Turn off the TV. Don’t buy the “education-based” video games. Love and praise your child. Play music you like for her (it does not have to be classical music). Explain everyday things to him. (Tell her why orange juice can sting a cut on a lip. Tell him why a hot stove must not be touched.)
Praise your young scientist for repeating things over and over. Play peek-a-boo and hide-and-seek. Enforce a healthy diet, and try for organic foods if possible. Use routine, with predictable consequences for behavior. Introduce math concepts. Sing the ABCs. Make sure your baby gets enough sleep.
-
Ages 2-7
Child should be exposed to new things-music, sports, subjects, activities. Keep reading aloud to your child, and praise her efforts to read to you. Talk to your child about why people behave as they do. Who makes the rules in society? Why? Buckle down on homework, establishing high expectations for work habits. Extra work (school worksheets during summer) is recommended in reasonable doses. Homework should not be a fight. If it is, talk to school teachers or a child psychologist.
This is the age that learning disorders can start to show. Get a handle on them early. If you have the opposite issue–your child wants to learn more than you can possibly teach–try to connect her to an expert in her field of interest. Perhaps a college professor would be willing to tutor your child for a couple hours on a weekend. Schedule playdates. Continue healthy sleep and diet activities.
At this age, children are scientists. Conduct fun and interesting household projects that help your child explore their world. Play guessing games such as, “I spy”, and “I’m thinking of something…” Do puzzles and card games.
-
Children 8-12
Encourage independent reading and books-on-CDs. Enforce healthy sleep and diet. Limit TV and video game time. Be an active participant in your child’s academics, remembering that you are doing him no favors by completing homework for him. Teach work skills, including: organization, time management, scheduling, focus. Praise your child for good report cards, but avoid monetary rewards for them. The goal is to help your child internalize the value of good grades, and not simply work for an external reward.
Listen to teacher’s feedback about any problematic academic or social behaviors. Listen to your child. Encourage her to pursue her intellectual passions (which may not be theoretical physics or advanced mathematical theory). Institute a “family game night,” where you play cards, puzzles, or other games that help build reasoning skills. Introduce your child to newspapers and have easy chats about what is happening in the world. Talk about governments, nationalities, and cultures.
Explain real-life issues like, “why do we keep our money in a bank?” “what should you do if a bully picks on you?” and “why does the guy from the gas company read our meter?”
-
Ages 12-18
Children become increasingly independent. The foundation for IQ is already set, but test performance can improve for some children. There is no substitute for attending school regularly, paying attention in class, and doing homework. These are musts. Keep a close watch on your child’s use of electronics. Phones, video games, and computers can interrupt sleep, cause social disruption, and distract children from work.
Help your child link her academic performance to her long term goals. Consider hiring a peer tutor, someone your child can actually tolerate. Help your child continue to build work skills such as organization, time management, avoiding procrastination, and breaking down big assignments into small “do-able” parts.
What Age Range Shows the Biggest IQ Score Changes
The biggest changes in IQ scores typically occur during early childhood, roughly between the ages of two and seven. This period is marked by rapid brain development and significant cognitive growth, which means a child’s intellectual abilities can vary quite a bit as they experience new learning and environmental influences. Factors such as nutrition, education, and family environment play a crucial role in shaping IQ during these formative years, leading to fluctuations in test results. As children grow older, especially after about age nine, their IQ scores tend to become more stable and consistently predictive of future intellectual performance. In adolescence and adulthood, changes in IQ are usually much less pronounced, with scores remaining relatively steady unless impacted by specific health or neurological conditions. This early variability reflects how dynamic cognitive development is in young children compared to the more established intellectual capacity observed in later years.
Key Points
- Early childhood (2-7 years): Largest fluctuations due to rapid developmental changes, environmental factors, and testing variability.
- Later childhood to adolescence: IQ scores tend to stabilize, with less dramatic fluctuations.
- Adulthood: IQ scores are relatively stable, with minimal changes unless affected by health or neurological factors.
Thus, childhood, particularly the early years, shows the most significant changes in IQ scores.
Which Studies Track IQ Stability from Infancy to Adulthood
Several long-term studies have been conducted to understand how intelligence develops and remains stable from infancy to adulthood. These studies often follow the same individuals over many years, assessing their cognitive abilities at different stages of life to see how early intelligence scores relate to later performance. Research has shown that IQ in infancy and early childhood is less stable because a baby’s brain is still developing and highly influenced by environmental factors such as nutrition, stimulation, and emotional support. However, as children grow older, particularly after age six or seven, IQ scores tend to become more consistent and predictive of intellectual performance in adulthood.
One of the most influential studies in this area was carried out in Scotland, where researchers followed a group of individuals who took intelligence tests as children in the 1930s and were retested decades later as adults. The findings revealed a strong correlation between childhood and adult IQ, suggesting that while experiences and education play roles in shaping intelligence, basic cognitive abilities show remarkable continuity over time. Other longitudinal studies, such as those conducted by psychologists like Nancy Bayley and Lewis Terman, have also demonstrated that early IQ scores, especially from middle childhood onward, tend to predict later intellectual functioning and academic success with reasonable accuracy.
Modern neuroscience has supported these findings by showing that the brain’s structure, particularly in regions related to reasoning and memory, develops steadily until adolescence, when it reaches a mature and more stable state. This biological maturation helps explain why IQ becomes more consistent from late childhood into adulthood. Although life experiences, health, and education can cause small changes in measured intelligence, the overall pattern of stability across decades highlights that IQ is both a reflection of inherited potential and the cumulative impact of one’s environment and learning experiences.
How do Environmental Factors Affect IQ Stability Over Time
Environmental factors affect IQ stability over time by influencing how much an individual can realize their genetic intellectual potential. While genetics lay the foundation for intelligence, environmental conditions such as the quality of parental education, family income, physical activity, and place of residence significantly impact IQ development, especially during childhood. Children raised in stimulating environments with access to educational resources, proper nutrition, and supportive social interactions tend to develop higher and more stable IQ scores over time. In contrast, children in impoverished or less enriched environments may have their cognitive potential limited, which can cause variability and less stability in IQ scores.
These environmental influences can cause fluctuations in early IQ measurements and affect the trajectory of intellectual development, but as children grow into adolescence and adulthood, the stability of IQ increases, reflecting the combined outcome of genetic predispositions and accumulated environmental effects. Overall, a nurturing and resourceful environment plays a crucial role in enabling stable and optimal IQ development across the lifespan.
