Poster #18 - The Tutoring Effect: The Potential Intellectually Stimulating Effect of Growing up in Families with Younger Siblings

• In Event: Poster Session 01

Abstract

Background: Intelligence has continually been found to be inversely associated with family size (Belmont & Marolla, 1973) (Falbo, 1978). Thus, it is expected that children without younger siblings (only children) have the highest intelligence because they grow up in the smallest families. However, Zajonc and Markus (1975) proposed the potential intellectually stimulating effect of growing up in families with younger siblings referred to as the “tutoring effect”, suggesting that children benefit intellectually from guiding and tutoring younger siblings in the early stages of life. The “tutoring effect” thus suggests that firstborn children with younger siblings do better intellectually than only children despite growing up in larger families.

Aim: To examine the potential intellectually stimulating effect of growing up in families with younger siblings in a large, representative Danish cohort. An additional aim is to analyze the potential “tutoring effect” according to the spacing between siblings to examine whether the age difference between siblings influences the potential “tutoring effect”.

Data: The project is based on Danish register data, with data on intelligence test scores obtained from the Danish Conscription Registry (DCR) for men invited to draft board examinations in Denmark from 2006 to 2019 (N=461,920). Unique personal identification numbers given to all citizens in Denmark enabled linkage between subjects from DCR and their biological parents and siblings.

Method: General linear models were used to estimate the potential intellectually stimulating effect of growing up in families with younger siblings by comparing men, with and without younger siblings, according to intelligence in young adulthood, adjusted for parental educational level, maternal age at birth, birth weight, and year of conscription. In addition, the potential "tutoring effect" was analyzed according to the spacing between siblings, ranging from 0-2 years to >6 years, among firstborn men.

Results: The mean IQ difference between firstborn men, with and without younger siblings, was 1.08 IQ points after adjusting for parental educational level, maternal age at birth, birth weight, and year of conscription (Table 1). On average, firstborn men with younger siblings had 1.08 IQ points higher intelligence in young adulthood than single children. The spacing between siblings appears to influence the intellectually stimulating effect of growing up in families with younger siblings. Firstborn men with 2-4 years younger siblings had 1.56 IQ points higher intelligence than only children, whereas firstborn men with 0-2 years younger siblings had 1.12 IQ points higher intelligence than only children (Figure 1). If the spacing between siblings increased to 4-6 years, the “tutoring effect” decreased to 0.34 IQ points and disappeared when the spacing between siblings exceeds six years (Figure 1).

Conclusion: The findings in this study support the apparent intellectually stimulating “tutoring effect”. Children with younger siblings have higher intelligence in young adulthood than only children despite growing up in larger families. The findings indicate that children benefit intellectually from growing up in families with younger siblings, especially if the age difference between siblings is relatively short (<4 years).

Authors

• Frederik Palmgren Kjaer, University of Copenhagen
  Presenting Author

• Gunhild Tidemann Okholm, University of Copenhagen

• Cathrine Lawaetz Wimmelmann, University of Copenhagen

• Merete Osler, Bispebjerg and Frederiksberg Hospitals

• Erik Lykke Mortensen, University of Copenhagen

• Trine Flensborg-Madsen, University of Copenhagen