In recent years, science teaching has mostly taken the form of inquiry. Thus, learners are more involved in the construction of their knowledge and skills, as these activities imply a constructivist approach. Although this method has shown certain advantages over traditional methods, it poses implementation difficulties for teachers. Moreover, different levels of guidance can be proposed, ranging from very closed inquiries, close to classic practical work, to more open-ended situations. In this paper, we are interested in the implementation of an inquiry by a secondary school chemistry teacher (year 10). We attempt to cross-reference qualitative data (observation of his classroom inquiry) with quantitative data collected from a questionnaire on his teaching. Is what the teacher does in the classroom consistent with what he says about his practice? How does he implement inquiry in his classroom session? We use the theoretical frameworks of PCK and the theory of joint action in didactics to try to answer our questions. This inquiry focuses on ion recognition tests conducted as a police investigation. This study shows that there is an inconsistency between what he implements in the classroom and his discourse on science teaching.