In education literature, there is a call for the development of pedagogical activities about socio-scientific issues, both for their affordance with the epistemic values of a renewed vision of science teaching (e. g. Driver, Newton, Osborne, 2000, Sadler & Zeidler, 2005), and for concerns of citizenship education (e. g. Legardez & Simonneaux, 2006). To develop high quality reasoning on such topics, fundamental knowledge on key scientific concepts together with socio-ethical beliefs, values and interests structuring the controversy must be taken into account (Oulton, Dillon, Grace, 2004, Albe, 2009). Contrary to mainstream traditional educational routines, the students are not expected to give a right or wrong answer and are required to use and confront various information sources (daily experience, the media, school knowledge, moral principles, cultural common sense, etc). From a corpus of videotaped scientific café-type debates about drinking water management, collected in schools in Mexico, the US and France, I analyzed the typical argumentative resources used by the students in such setting (emotions, norms and knowledge).In this presentation, the focus is on the pieces of knowledge that are co-constructed all along the activity, led by 15-17 year-old student moderators for 12-14 year-old student attendees. The emergence and evolution of two different micro-units of knowledge content (1. the use of water for the production of other goods and 2. the distinction between the cost and the price) were followed during the distinct steps of the café (alternation of quiz on basic knowledge, group discussion, and group and class debates on socio-scientific issues). In order to have a global temporal picture of the genesis of these pieces of knowledge, and a better understanding of moderators’ role in the process, these micro-units of content were also tracked on the video of the moderators’ training, which took place prior to the café. With the help of video annotation tools (Transana and ELAN), each occurrence of each micro-unit of knowledge was precisely characterized on a multimodal perspective. The coding scheme includes key lexical and structural elements, main gesture features, and the use of material resources in the pedagogical environment. The analytical tools were developed on the basis of previous literature on gesture analysis (e. g. Colletta, Ramona, Kunene, Venouil, Kaufmann, Simon, 2009, Cosnier, 2004, Kendon, 2004, McNeill, 1992, 2000) and empirical observation of the data. It serves as a basis to compare the multimodal trajectory of each micro-unit of knowledge, in different communicative contexts (quiz elucidation or debate on socio-scientific issues, linguistic and cultural environment, moderating style, type of knowledge involved). This contrastive stance leads to a discussion on whether some features of the multimodal scenario of emergence of a piece of knowledge can be considered determinant to fosters its elaboration and later reinvestment at different social levels (individual, small group, whole classroom).