Strong Genetic Contribution to Peer Relationship Difficulties at School Entry: Findings From a Longitudinal Twin Study


  • This research was supported by grants from the Fonds Québécois de la Recherche sur la Société et la Culture, the Fonds de la Recherche en Santé du Québec, the Social Science and Humanities Research Council of Canada, the National Health Research Development Program, the Canadian Institutes for Health Research, and Sainte-Justine Hospital's Research Center. Michel Boivin was supported by the Canada Research Chair Program. We are grateful to the children and parents of the Quebec Newborn Twin Study (QNTS), and the participating teachers and schools. We also thank Hélène Paradis and Bei Feng for data management and assistance with statistical analyses, and Jocelyn Malo for coordinating the data collection.

Correspondence concerning this article should be addressed to Michel Boivin, École de Psychologie, Université Laval, Pavillon Félix-Antoine-Savard, 2325 rue des Bibliothèques, Sainte-Foy, QC, Canada G1V 0A6 or Mara Brendgen, Département de psychologie, UQAM, C.P. 8888 succursale Centre-ville, Montréal, QC, Canada H3C 3P8. Electronic mail may be sent to or


This study assessed the genetic and environmental contributions to peer difficulties in the early school years. Twins' peer difficulties were assessed longitudinally in kindergarten (796 twins, Mage = 6.1 years), Grade 1 (948 twins, Mage = 7.1 years), and Grade 4 (868 twins, Mage = 10 years) through multiple informants. The multivariate results revealed that genetic factors accounted for a strong part of both yearly and stable peer difficulties. At the univariate level, the genetic contributions emerged progressively, as did a growing consensus among informants with respect to those who experienced peer difficulties. These results underline the need to intervene early and persistently, and to target the child and the peer context to prevent peer difficulties and their consequences.