In times of shortages in STEM professions, the untapped potential of girls with a STEM talent is a waste on a personal, social and economic level. Childhood is believed to be a very important formative stage in which children develop an early interest in specific occupations and teachers can have an important influence by developing lessons in such a way that girls are getting motivated for technology and/or science. This paper describes an educational design research study, in which we developed a checklist for teachers to screen the gender sensitivity of their STEM lessons and materials. The checklist contains 20 different questions categorised in four main pillars, namely: the fundamental critical attitude, the image of technology, guidance & interactions and didactical methods. Overall, the Gender-Sensitive Education Checklist (GSEC) can be used to tick what is already going well, ensure these roots can anchor strongly and focus on what teachers can do next to act in a more gender sensitive way. Preliminary evaluative findings suggest that the GSEC could potentially be an inspiring tool for teachers to continuously rethink their STEM lessons and materials. Further research is needed to test the effectiveness of the GSEC.