Pedagogical differentiation is a key to increasing school success. Yet examples of its use in the field are rare, and teachers question its feasibility. It also seems that teachers do not always receive adequate initial training on handling diversity. In this context, a researcher launched a study with 11 elementary school teachers in Québec to [1] understand how practitioners perceive differentiation in the classroom and [2] strengthen courses of action that could support training in this practice. The results suggest that a teacher who differentiates, practices with ideal interdependence and intercomprehension, fostering the explicit recognition, utilization and valuing of diversity, and openness to the legitimacy of a variety of teaching goals and methods. In terms of training, the results suggest that introspective work promotes openness to diversity. They also reveal five pedagogical criteria that can guide the work of the researcher-trainer in an action-training-research process: [1] make knowledge accessible, [2] promote involvement, [3] elicit cognitive dialogue, [4] favour knowledge restructuring and [5] support reflexive activity throughout the research process.