In the Storyline approach a fictive world is created in the classroom. Learners create and take on the role of characters in a story (lasting typically for four to six weeks), which develops as they work in small groups on practical and theoretical tasks linked to the curriculum. The approach offers conditions considered to promote second language development in young learners, namely an engaging, meaningful and motivational context in which communicative language skills are practised holistically. The word learners most commonly use to describe learning English through Storyline is `fun´; one aspect of the work which rates particularly highly is group collaboration. This presentation is based on a research study, Storyline, Our Sustainable Street, in which a class of Swedish 11-13 year olds created families who moved into a new street in a fictive English town. During the course of the Storyline the families took part in a project to live in a more sustainable way, and also had to deal with the problems of illegal rubbish dumping and anti-social neighbours. I will demonstrate how cooperative principles are integral to group tasks in Storyline and how, through cooperation, communicative language skills are developed.