This dissertation is about science education as an education for citizenship with a particular focus on the potential of inviting students to participate in critical examination of public issues in the media. Through digital media, a vast amount of health-related information is readily available to the public. People who turn to the Internet in search of health information of any kind, will come across a vast array of voices, information and contradictory claims. The rationale of this dissertation is the recognised challenges for citizens to stay critical when public issues that relate to health and nutrition are examined on the Internet. The aim of this dissertation is to contribute to expanding and nuancing the understanding of students’ critical examination of public issues in science education by drawing on a capabilities approach. Philosopher Martha Nussbaum’s version of the capabilities approach and notion of ‘world citizenship’ is situated in science education and used for analysing students’ participation in critical examination of public issues relating to health. In addition, sociocultural perspectives are drawn upon to conceptualise learning. The dissertation builds on two different research projects, both conducted as design-based research collaborations with upper secondary school science teachers and their students. The data are comprised of audio and video recordings of student group discussions as they search for and critically examine health-related information on the Internet, and video recordings and field notes from the teachers’ whole-class introductions to the activities. Data have been analysed using qualitative content analysis, also drawing on the work of Nussbaum. The findings in this dissertation are presented in four papers. Paper I reports how the introduction of an evaluation tool afforded and constrained students’ critical examination of health issues on the Internet, and how this process can be fruitfully analysed by taking a capabilities approach. The findings show how use of the evaluation tool caused students to privilege scientific information, leaving lived experiences of health issues and students’ own purposes of the information-searching unexamined. Paper II focuses students’ critical examination of controversial and emerging science reported in news media. The findings illuminate how students’ encounters with a controversial nutrition study on the Internet triggered epistemological work — the examination of scientific knowledge as embedded in social, cultural and historical practices. Paper III focuses students’ critical examination of a science-laden public issue concerning milk consumption. The findings show how the students examine their own and societal moral underpinnings of consuming milk, and how the production and consumption of milk affect people's lives and the places we live. In these conversations on milk, the students also imagine different sustainable futures. Paper IV proposes a heuristic for ethical reflection on participatory science education research, highlighting reflective questions in relation to the dimensions of ontology, epistemology and methodology. It is intended to extend standard ethical reflection in education research by taking hierarchies, roles, values, risks, objectives and accountability into account. Overall, the results reported in this dissertation emphasise that students’ critical examination of public issues in the media cannot be limited to source critique that aims to sift out ‘facts’ and uncontested science. This dissertation illuminates the potentiality of science education for citizenship in providing students with opportunities to participate in critical examination of themselves and society in encounters with issues of public concern.