Here is the design of a clinical trial:

Official Title: Organizational Skills Training for Children With ADHD

Included conditions:
- ADHD

Study Armgroups:
- {'label': 'Intervention', 'type': 'EXPERIMENTAL', 'description': 'The participants in the intervention group will receive treatment as usual + 10 sessions of organizational skills training', 'interventionNames': ['Behavioral: Organizational skills training', 'Other: Treatment as usual']}
- {'label': 'Control', 'type': 'OTHER', 'description': 'Control participants will receive treatment as usual.', 'interventionNames': ['Other: Treatment as usual']}

Interventions:
- {'type': 'BEHAVIORAL', 'name': 'Organizational skills training', 'description': '10 sessions of parent and child training in a group format.', 'armGroupLabels': ['Intervention']}
- {'type': 'OTHER', 'name': 'Treatment as usual', 'description': 'Treatment as usual in the outpatient clinic', 'armGroupLabels': ['Control', 'Intervention']}

Primary Outcomes:
- {'measure': 'Children Organizational Skills Scale (COSS)-parent', 'description': 'organizational skills questionnaire', 'timeFrame': 'after 10 weeks of intervention'}

Please estimate the sample size based on the assumption: 
90% power and 5% significance level for primary outcome; 80% power and 5% significance level for secondary outcomes; 10% expected dropout rate.
Sample size
          We are conducting a randomized controlled trial using the continuous response variable COSS-total parent rating from independent control and experimental participants allocated at a 1:1 ratio. The primary outcome measure COSS has been tested in previous trials [30, 31].
          Using data from Pfiffner and colleagues [31], we conducted a sample size calculation based on the COSS total score by parent rating as primary outcome. Based on a minimal relevant difference of 0.30 and a standard deviation of 0.36, it requires 32 participants in each group to reach 90% power with 5% significance level. Furthermore, to have sufficient power to analyze secondary outcomes with standardized effect size 0.5 SD, the required sample size was doubled to n = 64 in each group, resulting in 80% power for the secondary outcomes using 5% significance level. Finally, to account for an expected dropout of 10% during the study period, the required sample size was increased to 71 in each group (total sample size n = 142).