This paper addresses the issue of assisting observation and analysis of learners’ behaviour. Our goal is to propose models/tools to facilitate these tasks for the trainer. We propose an approach based on the exploitation traces. The trace represents learners’ practices within learning environments. The principle is to transform traces of low abstraction level to build higher-level information that reflects the learner’s behaviour. Our work is part of a project in partnership with the EDF Group aiming to assist trainers in observation and analysis of trainee operators for driving activities on nuclear power plant fullscale simulator. We developed a platform D3KODE that implements our models. D3KODE allows storage, processing and interactive visualisation of traces, and has been experimented with EDF Group experts, trainers and trainees. The result demonstrated D3KODE helped the trainers to confirm/validate more easily realisations and no-realisations of educational objectives trainees and facilitated the exchanges between tutors and trainees.