Learning Design increased the hope of sharing and reusing TEL units of learning. However, appropriating a learning design remains difficult for teachers. A first issue concerns its transparency in terms of, motivation, knowledge at stake, structuration choices, or justification of its accomplishment. A second issue concerns its richness in terms of means of observation allowing teachers to infer pathways taken by learners at runtime. Our research works directed by “co-design learning with teachers”, led us to propose a generic model for situations engaging learners to solve a well-defined problem. This model puts forward the benefits of integrating into the learning design both observables on the effective learning situation and teachers’ professional knowledge explicating the learning design components. Thus, teachers might be helped to plan its use, potentially suit it for his or her teaching needs, and also follow the learners’ progression towards its achievement. Implementation in FORMID is further discussed.