This study assesses the development process of a tool to measure students' perceptions of gender mainstreaming in STEM (Science, Technology, Engineering and Mathematics) studies. Within the framework of a pilot project named Gender Dimension in Teaching implemented at the Universitat Politècnica de Catalunya, UPC-BarcelonaTech, a group of 35 lecturers worked during one semester on how to introduce the gender perspective in their teaching. The project focuses on the four pillars of teaching (i.e. contents, classroom management, methodology and assessment), which were revised from a gender perspective. Within each pillar, gender issues were identified according to the experienced perception of the project participants. However, uncertainty aroused concerning the reliability of such a perception. Indeed, teachers' perception might be influenced by stereotypes and prejudices that could alter the identification of gender issues. Hence, it became obvious that more reliable data concerning students' perceptions was needed. To this end, a first test was cooperatively developed using Google Forms. The survey was tested at the beginning of the semester in 8 different UPC degrees, both at Bachelor and Master level, obtaining more than 500 answers. Despite some interesting preliminary results, a detailed revision of the questionnaire was conducted in order to remove some acquiescence bias and formal errors, thus improving the quality of the survey for a more global study. The improvement process included discussions among the members of the Gender Dimension in Teaching project, discussions with some UPC students' associations and suggestions form experts in survey definition. The revised questionnaire was tested and discussed with a small sample of students. As a result, an improved questionnaire to assess student's perceptions of gender mainstreaming in STEM studies has been cooperatively obtained, which may become an essential tool for further studies extended to all the university community.