The interaction analysis of the students who take part in the
class with the teacher is insufficient to show how each classroom student
contributes to the interaction and how he or she is affected by it. This article
reports some results of a research conducted in an elementary school
eighth grade class, in which the students could observe and explain a given
phenomenon, individually and collectively. The individual trajectory analysis
of two students showed that both individual explanations, initially different
from each other, were modified during the interaction with the teacher and
the colleagues.