A Cluster-RCT of SHS Among Primary School Students

Worksheets will be distributed to students for them and their parents to complete together. During the first 3 months, the teachers will distribute 1 worksheet every two weeks to the intervention grades, and 1 worksheet in the 4th and 5th months as boosters. The worksheets will deliver information about tobacco smoke, SHS and THS, inviting students and their family members to complete other interesting tasks together.

A mobile phone number of this study is also provided on the worksheets, through which participants can receive WhatsApp/WeChat/instant messages (1-2 times every week) designed to encourage behavioural change \[15\]. They can then forward selected messages to other members of their household, especially smokers.

At the end of each worksheet, a QR code is inserted. By scanning this code, students or parents will be invited to answer 2-3 simple quizzes which allow us to assess students' knowledge obtained from the intervention materials and their avoidance of environmental tobacco smoke.

A leaflet on smoking and SHS published by the Department of Health will be mailed to the control grades.