Research and design activities are important focus points in international policies for secondary Science, Technology, Engineering and Mathematics (STEM) education. It is up to school teachers to implement and supervise these activities in the STEM classroom. However, not much is known about the attitudes teachers hold towards supervising research projects or design projects. In this study, a questionnaire to measure teacher attitudes towards supervising research activities and design activities in secondary school was completed by 130 Dutch teachers who taught the relatively new Dutch STEM subjects O&O (research and design) and NLT (nature, life, and technology). These integrated STEM subjects are project and context based and are taught in a limited number of schools. Important differences between these integrated STEM subjects are their student and teacher populations: NLT is taught in grades 10–12 by teachers with a qualification in a science subject, while O&O is taught in grades 7–12 and can be given by any teacher in secondary school. The results showed that on average, both O&O and NLT teachers had high self-efficacy scores on supervising research and design projects even when they had received no special education in doing so. Furthermore, the teachers in general viewed supervising research projects as a more relevant activity than supervising design. Since research and design activities are becoming more important in (inter)national curriculum standards, STEM teacher education and subsequent professional development should not only familiarize teachers with supervising research projects, but with design projects as well.