The products of modern biotechnology processes such as genetic engineering, DNA testing and cloning will increasingly impact on society. It is essential that young people have a well-developed scientific understanding of biotechnology and associated processes so that they are able to contribute to public debate and make informed personal decisions. The aim of this study was to examine the development of understandings and attitudes about biotechnology processes as students progress through high school. In a cross-sectional case study, data was obtained from student interviews and written surveys of students aged 12 to 17 years. The results indicate that students' ability to provide a generally accepted definition and examples of biotechnology, cloning and genetically modified foods was relatively poor amongst 12-13 year old students but improved in older students. Most students approved of the use of biotechnology processes involving micro-organisms, plants and humans and disapproved of the use of animals. Overall, 12-13 year old students' attitudes were less favourable than older students regardless of the context. An awareness of the development and range of students' understandings and attitudes may lead to a more appropriate use of biotechnology curriculum materials and thus improved biotechnology education in schools.