This case study describes a classroom-based questionnaire that was carried out with a group of 36 high school students (17-18 years old) in Catalonia. The aim was to examine the usefulness of questionnaires focused on scientific inquiry, both to evaluate students' inquiry abilities and for their potential as tools to improve the understanding of these processes. The questionnaire refers to procedural understanding within the field of enzyme kinetics. Rubrics for scoring the questionnaire were developed to standardise data analysis. Results showed ambiguous identification of the inquiry question and difficulties in formulating accurate hypotheses and identifying the independent variable. The greatest difficulties appeared in the control variables and the methodology design; misunderstandings related to the underlying scientific concepts were also identified. Questionnaires like the one used in this case study can be useful tools for formative assessment and allow fundamental aspects of scientific inquiry processes to be tackled in less time because they do not involve hands-on activities but instead combine scientific practices with core disciplinary ideas.