A growing body of research in developmental psychology and behavioral economics is revisiting a long-standing question: do firstborn children have measurable cognitive advantages over their younger siblings? New analysis drawing on work from the University of Edinburgh and complementary studies published through the National Bureau of Economic Research (NBER) indicates that the answer is yes—but with important qualifications.
While the effect exists, it is modest, and birth order explains only a small portion of overall differences in intelligence or academic achievement.
Findings from the Edinburgh Study
Researchers associated with the University of Edinburgh linked large-scale national survey datasets with detailed family structure information, enabling them to track thousands of children from infancy through early childhood. The data showed:
- Firstborn children scored slightly higher on cognitive assessments—including early IQ-type tests—from as early as one year of age.
- Parents reported providing similar levels of emotional warmth to all children, suggesting that differences in affection or attachment were not the key drivers.
- However, firstborns received more early cognitive stimulation, including:
- More time spent reading
- Structured teaching activities
- Greater engagement in educational games and cognitively rich play
These inputs—collectively referred to as “mental stimulation”—are known predictors of early cognitive development.
The study suggests that the timing of parental investment may matter more than previously understood. Firstborns benefit from a period of undivided parental attention before younger siblings arrive.
The Role of Parental Attention and Investment
The results support a consistent pattern found in developmental economics: differences in one-on-one learning time help explain small but measurable birth-order effects.
However, the effect is far from large. Research using Scandinavian military conscription data—among the most comprehensive IQ datasets globally—finds an average:
- Approximately 3-point IQ difference between firstborn and second-born children
This gap is statistically significant but modest, meaning:
- It cannot meaningfully predict future academic, economic, or life outcomes for any individual child.
- It accounts for only a small fraction of the total variation in intelligence within families.
In other words, while the average trend exists, it is not a dominant factor in real-world performance.
Insights from NBER Birth-Order Research
Several influential NBER papers—including “Older and Wiser? Birth Order and IQ of Young Men”—have produced results closely aligned with the Edinburgh findings. These studies analyzed data across thousands of sibling pairs and found that:
- Earlier-born children tend to have slightly higher IQ scores.
- Firstborns often exhibit better educational outcomes, such as higher grades or greater likelihood of completing tertiary education.
- Differences in parental time investments and expectations appear to be key mediators.
NBER studies also explore birth order effects on non-cognitive skills, such as conscientiousness, risk preferences, and social behavior, finding that these traits can vary systematically based on family dynamics and early responsibility roles.
Limits, Misconceptions, and Important Nuance
Experts emphasize that birth order should not be viewed deterministically. Several points underscore the limits of the effect:
- Birth order explains only a very small share of total IQ variation.
Genetics, environment, nutrition, quality of schooling, and home learning conditions all play much larger roles. - Later-born children often outperform firstborns, especially in households where:
- Parents maintain strong educational engagement across siblings
- Younger children learn by imitation from older siblings
- Family resources and stability increase over time
- Family size and socioeconomic status influence birth-order effects, meaning results should not be overgeneralized.
The consensus across studies is that birth order produces average tendencies, not rigid outcomes.
