Drawing on error analysis, this paper investigates the idea that every process of student or teacher (self)evaluation can be considered a useful formative experience. The (self)evaluation approach shown in this paper has been applied to a course of E/LE for Italian university students. Students, who identify and correct their classmates’ mistakes, are thus encouraged to reflect more carefully on their own ones. This activity constitutes a valuable tool to gather information on the learning process: today in fact many tools, such as the Portfolio, are available to evaluate teaching quality and student achievement. According to self-assessment and reflective practices, the teacher can thus reflect on his own classroom activities in order to reconsider her/his professional skills and develop new teaching strategies.