This was a qualitative study. We conducted three repeat in-depth interviews with 26 trial participants over the duration of the trial (2011-2014) from both the SCT and control (continuous therapy) arms. These interview were conducted towards the start of the trial, during the second half of the trial and during the process of being moved into the follow-up stage of the trial. There were two other sites connected to this study (UK and USA), funding for which came from different sources. 43 young people were involved in total in the interviews.
 
 We adopted a purposive sampling approach to reflect the diversity of the trial population in terms of sex, age and ethnicity. Participants were also invited to keep an audio diary, however we found this to be very challenging in this setting as although enthusiastic participants were not confident that they could keep their diaries safe once recorded and so generally chose not to use them. We also invited young people to keep a written diary should they have wanted to. No participants took up this opportunity. 
 
 With the permission of the young people, we conducted 15 interviews with a subsample of their carers. We adopted a theoretically informed approach to our carer sample to include a wide range of carer/s, including non-biological carers, and circumstances. 
 
 We also conducted 4 focus group discussions (2015) with 24 young people after they had been notified of the trial results to explore their reactions and attitudes towards SCT being rolled-out more broadly. Of this 24, 18 had been involved in the qualitative interviews through the trial and 6 trial participants were also included who had not previously been involved.