Improving teaching is a central issue of concern to the Institution, trainers and researchers. Our study focuses on the area of documentary reading in the 3 cycle. We present a possible response, called the continuous design of a tool, which would allow teachers to develop their professional skills. This approach involves researchers and practitioners in the co-design of this tool. The central character of this co-design is called the Knowledge Passer. It makes the link between these two communities. It translates knowledge and know-how, drives the debate around the construction of the tool. It then summarises the results and makes choices to develop the tool under construction, known as a borderline object, to make it more useful, usable and acceptable. We show how the passers-through can encourage practitioners to develop their professional skills in teaching documentary reading strategies, through the implementation of this approach. The methodology is based on semi-directional interviews before and after the tool test, classroom observations, co-designer meetings and a final self-assessment of practitioners. Lexical analysis and simplex based on the data collection validated the hypothesis of improved knowledge on the learning and teaching processes of documentary comprehension strategies in the 3 cycle for practitioners. The smuggler has led them to develop their professional skills and to analyse their practices. At the same time, the innovative tool is improved by analysing teachers’ feedback to make it more useful, usable and acceptable.