age of 22 years and 3 months, SD = 7.5 months, and the second at age 23 years and 4 months, SD = 7.8 months). In Grade 11, 72.2% of participants brought a friend in our laboratory to participate in an interaction task, and on that occasion, we were able gather friends’ report on their own substance use for 64.0% of participants. Also in Grade 11, the rate of completion of an effortful control measure by parents was at 68.5%, and it was at 66.7% for the teacher report. Overall in Grade 11, 49% of the sample (489 participants) had complete data on all measures at that assessment point.
