This thesis is about Swedish secondary sexuality education with a particular focus on the becomings of natural science and pornography education. Recent scrutiny of the knowledge area has stressed the need for teaching to include student perspectives, cover more than mere medical and biological knowledge, and be more affirmative. Accordingly, the main aim of this thesis has been to investigate the becomings of lower and upper secondary sexuality education with a practice-based approach. A second aim has been to explore how the onto-epistemological framing could contribute to new understandings of what sexuality education could be and to make proposals for the teaching and learning of the knowledge area. Here, the theoretical positions offered by Karen Barad and Donna Haraway were used in analysis of teacher and student discussions on various phenomena related to sex and sexuality. The four studies forming the basis of this thesis further build upon engagements with four different schools—two lower and upper secondary settings, respectively. Data were produced through notes and audio recordings where the teachers discussed the construction of sexuality education, or from actual teaching in a class and student interviews. Study I engages with the teaching of genital anatomy and upper secondary students’ notions of virginity. The results suggest that teaching should engage with a variety of perspectives, for example, traditions, norms, and values with regard to virginity. Study II focuses on upper secondary student engagements with contraceptive methods, in particular, the use of hormonal contraception and a mobile phone contraceptive application. The results show the need for teaching to problematise possible side effects of various contraceptive methods, and contraceptive responsibility. Study III breaks with the natural science framing and engages with an interdisciplinary teacher collaboration concerning education about pornography. The topic came into being as somewhat troublesome, having had too great a focus on the teaching, and it is therefore suggested that the topic be part of a wider context addressing gender equality, relationships, sexuality, communication, and consent. Study IV returns to the teaching of natural science sexuality education, but from a more general perspective. In this study, the teachers found ways to invite students to be part of the unfolding of the teaching and to challenge heterosexual and sex-negative premises common in sexuality education in Sweden and worldwide. Overall, in the four studies, sexuality education was enacted as a highly relational and explorative practice. Encounters with primarily the material world, but also time and space, further made teaching more student centred. It is suggested that sexuality education moreover not only be taught as a medical and biological phenomenon, but also in entanglement with perspectives on culture, religion, history, tradition, and societal norms.