This study deals with the dynamics of evaluation at work in a collaborative experiment carried out with two multidisciplinary teams of French middle-school teachers. It shows how connecting the teachers’ experience with the outside frame of reference, through a reflexive, critical, but also prospective approach of assessment for learning (AfL) methodology, produces both referentialization and subjectivization/intersubjectivization, enabling individual and collective professional development. Collective creation of a common frame of reference through students’ elaboration and usage of criterion-based assessment grids brings about varied implementations and understandings among teachers when the evaluation is actually conducted. Experimenting this hybrid construct in the classroom and discussing it by confronting the activity’s actual outcome with its projected result open new insights and perspectives that lead to a broader referentialization of AfL and renewed professional identity.