Experimental design learning activities have been shown to foster the acquisition of scientific abilities and to favour sense-making. A teaching sequence is proposed to second year university students whose goal is to make them experience experimental design and reflect on the design process. The writing part of the students' design work is supported by a computer-based platform, LabBook, devoted to experimental design work. Students go through three experimental situations that are organized in a role-playing game. They have to design an experiment and to write the procedure that will be performed by another student. The students' reflections, collected in written reports, are analysed using a list of criteria that were designed for experimental procedures assessment. Reflecting on their successive roles as designers, technicians and silent observers, the students become aware of experimental design stakes. Observing a technician who tests the experimental procedure appears very efficient for experimental assessment and it does help students to gain assessment skills. The role-playing game makes them focus particularly on the communicability qualities of a written procedure. Since the procedure must lead the technician to collect the expected results successfully, the designers deal with communicability together with executability (feasibility, temporal and safety constraints) and data quality aims. The students point out accurately the difficulties of writing tasks, especially the balance between concise and complete or detailed description. The procedure editor of LabBook, Copex, appears very useful to them, being able to fulfil their requirements for organising and documenting a written experimental procedure. The role-playing game incites the students to deepen the scientific reflection and improves the organisation of their work. However, relevance criteria are more difficult to grab and fulfil. The experimental situations do not have the same ability to reveal these criteria to students and to make them reflect and evolve.