This article discusses the findings of a survey of centres using the "Twenty First Century Science" suite of GCSE courses, focusing on the impact of its introduction on the number of students beginning AS-level courses in the sciences. The data indicate increases of 24% to 38% in the numbers beginning AS-level courses in the three main sciences in 2008 in these centres. This provides striking evidence that GCSE courses which highlight the relevance of school science to out-of-school contexts and encourage discussion of socio-scientific issues, whilst also treating key theoretical ideas in the sciences in depth, increase student engagement and the numbers choosing to continue the study of science. (Contains 5 tables.)