It is broadly admitted that social contexts of reasoning may prompt children and adolescents to improve the quality of their reasoning. However, it is not clear how this quality may be assessed when it comes to arguments expressed within oral interactions in diverse settings (whole-class or small-group discussions) by students of different ages and cultural backgrounds. This study aims to offer a methodological contribution to the issue of oral argument assessment of children and adolescents, by looking at a large, annotated corpus of dialogic discussions during 111 lessons taking place in five countries. Our analysis combines a structural (Toulmin Argument Pattern) and functional (Walton's argumentation schemes) approach to argumentative reasoning. Our findings show significant variations across age groups and social settings. The discussion points out the importance of sociocultural framing of argument reasoning development and the continuation of research in argument assessment methods able to grasp important developmental and cultural variations.