Objective: The Scale of Emotional Development--Short (SED-S) is an instrument to assess the level of emotional development (ED) in people with intellectual and developmental disability. Index cases are developed as a didactic tool to standardize the application of the scale. Method: In a stepwise process, a European working group from six countries developed five index cases, one for each level of ED. All cases were first scored by 20 raters using the SED-S and then rephrased to reduce inter-rater variations (SD > 0.5). Results: All five index cases yielded overall ratings that matched the intended level of ED. Across the range of ED, "Regulating Affect" needed rephrasing most to ensure a distinct description within each level of ED. Conclusions: The tri-lingual, cross-cultural evolution of five index cases contributes to a standardized application of the SED-S and can serve as training material to improve the inter-rater reliability of the SED-S across different cultures and languages.