In Bangladesh, second-hand smoke (SHS) is recognised as a principal source of indoor air pollution and a major public health concern. A recent community survey of 722 households in Bangladesh revealed that smoking indoors was a common practice, with more than half (55%) of the households having at least one smoker. A majority of these smokers did not practice smoking restrictions at home (including smoking in front of children), exposing almost 40% of the children to SHS. In this study we aim to reduce children’s exposure to SHS in their homes. The salient objectives of CLASS Bangladesh study are; (i) to develop a school-based intervention to enable children as agents of behaviour change; (ii) to pilot test the developed intervention; and (iii) to test its effectiveness and cost effectiveness in reducing SHS.