Maartje Boer

THE COURSE OF PROBLEMATIC SMU 199 7 SMU and SMU frequency did not vary across the two subsets, suggesting that the distributions of the trajectories were comparable (Appendix, Table A7.1). Hence, merging the two samples was justified. Within the analysis sample, students were on average 12.511 years old ( SD = 0.602) in T1, 45.9% was girl, and 21.9% had an immigrant background. Among adolescents with an immigrant background, 45.2% had one parent that was born in Suriname, Netherlands Antilles, Morocco, Turkey, or another country, and their other parent was born in the Netherlands. The other 54.8% had two parents from these or other countries. In addition, students followed different educational tracks according to the Dutch education system, namely pre-vocational ( VMBO; 57.8%), intermediate ( HAVO; 28.5%), and pre- university ( VWO; 13.7%). The present sample composition differed somewhat from the Dutch school population with respect to educational level: 13.7% among sample participants versus 20.6% in the Dutch 10 th -grade population in 2018/2019 (Central Bureau for Statistics, 2021). Participation rates at T1 until T4 were 55.1%, 93.5%, 75.9%, and 34.9%, respectively. The reason why data were not complete in T1 was because some students’ first participation was in T2 or T3. Nevertheless, all students were enrolled in the same grade at each assessment. There was considerable dropout among students attending pre-vocational education: Of all adolescents participating in T4, 19.6% was pre-vocational student, while of all adolescents participating in T1, this was 60.6%. This dropout was mainly due to dropout of entire pre-vocational schools, school years (e.g., final exam years), or school classes (e.g., because teachers were not able to schedule the survey assessment), and not due to individual selection. Prior to each survey assessment, parents received a letter which informed them about the study and provided them with the opportunity to refuse participation of their child via email or telephone call. Also, prior to each survey round, students were informed about the purpose of the study, that participation was voluntary and anonymous, and that they could withdraw their participation at any moment. Both parents and students received this information two weeks before the first day of data collection. The assessments were administered in the classroom through digital self- completion, whereby research-assistant monitored and assisted students where necessary. The assessments were carried out in accordance with the