The coaching and assessment of preservice teachers during teacher training internships are very demanding tasks that are put in the hands of cooperating teachers. When the student teacher encounters difficulties, the cooperating teacher, this “field trainer”, may doubt of his own abilities, question the legitimacy of his role and lead him to look for resources and better approaches. This paper presents the results of a study conducted with teachers who supervised students who were facing difficulties. An analysis of their comments reveals their pattern of coaching and assessing and shows that they start to judge as soon as the process starts and that they fully assume their role as assessors.