Purpose: Owing to its complexity, sustainable development (SD) cannot be simply integrated as a supplementary course within the engineer's curricula. The first aim of this paper is to focus on how to reflect pedagogically this complexity. After dealing with these questions, the paper aims to present a tool that can evaluate the student's understanding of SD concepts. Design/methodology/approach: A method of analysis of a student's sustainability's comprehension, based on cognitive maps, has been developed. The students are asked to write and connect by arrows all the terms that they associate to the concept of SD. The assessment of the aforementioned cognitive maps is based on an approach via semantic category. Findings: This study shows that the students' perception of SD before the training seems mainly focalised on environmental and economical aspects. After the SD course, an increase of the number of words quoted is noted for each category (social and cultural aspects; stakeholders, principles of SD and allusions to complexity, temporal and spatial dimensions). Their vision seems richer and wider. The training seemed successful to help the students who did not associate SD to diverse dimension to improve this perception. Practical implications: This cognitive map method can be a useful tool to improve learning in quantitative terms but also in qualitative terms. Identifying knowledge gaps and misunderstood ideas allows the improvement in the training. Originality/value: This study presents a new method that can be used to evaluate the impact of training sessions on students. Another advantage is to analyse how the student's knowledge are interconnected. This seems particularly interesting because the study of this transdisciplinary concept as well, necessitates an integrated vision. (Contains 10 figures and 3 tables.)