Twins have similar academic performance to single-born children, finds a large Danish study published online by the BMJ today.
These findings challenge earlier research that show twins have considerably lower IQ in childhood than singletons.
Using the Danish national birth register, researchers identified 3,411 twins and a random sample of 7,796 singletons born in Denmark during 1986-8. They also gathered information on birth weight, gestational age at birth, and parents' age and education.
At ninth grade (age 15 or 16), they analysed school test results and found almost identical scores for twins and singletons, despite the twins weighing on average 908 g less than the singletons at birth. In fact, twins did slightly better in mathematics than singletons.
Taking into account factors such as the child's sex, age at test, birth weight, and parents' education made little difference.
Birth weight had a minimal effect on test scores although twins of extremely low birth weight more often did not have a ninth grade test registered.
The authors suggest that better obstetric and paediatric practices over the past 50 years have improved the cognitive disadvantage identified in twins by earlier research.