School performance at ages 12 and 14 was reported by the twins’ teachers (see below) as part of a behavioral assessment. The teachers’ reports were associated with some missing data at age 14, because many twins were unable or unwilling to nominate a teacher who knew them well. In contrast, at age 12, the twins had a single main teacher who was contacted with parental permission. Parental covariates (see below) were not available for 532 twin individuals from 274 families. Accordingly, path models adjusting for parental factors were based on a total of 4,761 individuals (2,354 or 49.4% females).
