© 2022, The Author(s), under exclusive licence to Springer Nature B.V.Some of the key challenges for STEM education in Turkey include the problems encountered by teachers when integrating diverse disciplines and technologies into STEM activities, the need for teachers to acquire the skills necessary to prepare and implement appropriate STEM activities for the educational level of their students and their school context, the difficulties faced by teachers when following the Engineering Design (ED) problem-solving process in the implementation of STEM activities, and teachers’ heavy workloads, which impede the collaboration required to develop and implement STEM activities. A field study was carried out in Samsun, Turkey between 2017 and 2018 to develop a Design Thinking (DT) approach customized to support STEM teachers. The field study adopted an action research methodology and involved two main studies with fifth-grade teachers and students, facilitated by a researcher-designer. Qualitative methods including co-design workshops, focus groups, interviews, and observation were employed to gather data. The paper presents a seven-step DT approach, customized to support pre-service and in-service secondary school teachers in collaboratively designing and implementing classroom STEM activities. The results indicate that structuring the STEM activity design as a specialized DT process provides a complementary framework. Collaboration among teachers in a structured STEM activity design process supports the integration of disciplines and the development of STEM activities that correspond to the students’ level of knowledge and ability. Empathy building, which facilitates familiarization with other teachers and students, enhances collaboration among teachers and aids the development of STEM activities relevant to the students’ level.