This presentation focuses on “Cooperative Engineering”, in which teachers and researchers co-design didactic sequences. We describe Cooperative Engineering by situating it in reference to various traditions of research, and we show how it can be included within a clinical research approach. Then, we outline some main dimensions of a theoretical frame, stemmed from comparative didactics, the Joint Action Theory in Didactics (Ligozat, 2011; Tiberghien & Malkoun, 2009) on which we rely to build and study different designs in the cooperative engineering process. The third part pertains to the empirical study of two Cooperative Engineerings. The first one, Treasure Game, is grounded on to the communication of graphical representations at Kindergarten. The second one, Arithmetic and Comprehension at Elementary School (ACE) is based on the building of a curriculum at First Grade in mathematics (numbers). We describe in particular the way in which the production of work hypotheses aimed to be tested in these designs. Then we document the way in which this process is gradually shared between teachers and researchers. We analyze the nature of the common knowledge built in this process.