Game elements are rarely explicit when designing serious games or gamified learning activities. We think that the overall design, including instructional design aspects and gamification elements, should be validate by involved experts in the earlier stage of the general design & develop process. We tackle this challenge by proposing a Domain-specific Modeling orientation to our proposals: a metamodeling formalism to capture the gamified instructional design model, and a specific validation process involving domain experts. The validation includes a static verification , by using this formalism to model concrete learning sessions based on concrete informations from real situations described by experts, and a dynamic verification, by developing a simplified simulator for 'execut-ing' the learning sessions scenarios with experts. This propositions are part of the EmoTED research project about a learning application, the mimicry of emotions, for children with ASD. It aims at reinforce face-to-face teaching sessions with therapists by training sessions at home with the supervision of the children's parents. This case-study will ground our proposals and their experimentations.