Our works take place in the research field of Technology Enhanced Learning systems engineering. In this paper we deal with the design rationale of open pedagogical scenarios (OPS). We have proposed a generic model of OPS based on the QOC formalism, and an incremental/iterative engineering process of OPS. In order to provide the dedicated supports for practitioner teachers/designers we have followed a constructive approach of instructional design based on Model- Driven Engineering and Domain-Specific Modeling. To verify our proposal we took Hop3x domain as experimentation area. The Hop3x’s DSEML is described by a metamodel of open learning sessions which is defined basing both on the generic model of OPS and Hop3x-specific educational domain semantic, and accordingly a graphical editor of sessions has been developed thanks to EMF/GMF tooling.