Abstract
The most part of teachers' knowledge updating takes place through self-study. This article questions the role of information skills in the professional development of teachers confronted with situations of unprecedented change. Based on the documentational approach to didactics and professional didactics, we propose to analyze the activity of three teachers, through a model of documentational expertise. We found the driving role of the activity of designing a new lesson in the development of new knowledge, an activity that relies on the information and digital culture of the teachers monitored.