Although the term "scientific literacy" has been increasingly used in recent years to characterise the aim of school science education, there is still considerable uncertainty about its meaning and implications for the curriculum. A major national project in England, "Twenty First Century Science", is evaluating the feasibility of a more flexible science curriculum structure for 15-year-old and 16-year-old students, centring around a core course for all students with a scientific literacy emphasis. Over 12,000 students in 78 schools have followed this course since September 2003. The development of a detailed teaching programme is an important means of clarifying the meanings and implications of a "scientific literacy" approach. Questionnaire data from teachers at the end of the first and second years of the project (N = 40 and N = 51) show a strongly positive evaluation of the central features of the course design. Teachers perceive the scientific literacy emphasis as markedly increasing student interest and engagement. Key challenges identified are the language and reasoning demands in looking critically at public accounts of science, and the classroom management of more open discussion about science-related issues. (Contains 13 tables and 2 figures.)