accordingly, teachers generally know their students quite well. All twins were sent a follow-up questionnaire within 3 months of the date they reached age 14 (mean age at response 14.1 years, SD = 0.1). Of the 2,567 twin pairs who completed questionnaires at age 12, both co-twins in 2,355 of these pairs (92%) later completed the age 14 follow-up.
