ABSTRACTComplex competences, such as managing students' aggressive behaviour, are challenging to develop during teacher training. Recently, video‐based simulations have been considered promising, yet suitable assessment instruments are limitedly available. This paper reports on the design and evaluation of a video‐based assessment tool tailored to measure preservice teachers' verbal aggression management competence (V‐AMC) development. Design considerations for video‐based activities served as a framework, resulting in an assessment instrument consisting of video vignettes mirroring classroom situations concerning verbal aggressive behaviour, questions prompting situation‐specific skills development, and a coding scheme to analyse preservice teachers' answers. Furthermore, this paper discusses the results of the instrument's implementation on preservice teachers' (n = 182) V‐AMC. Findings support the appropriateness of the instrument in assessing V‐AMC levels and mapping the impact of a simulation‐based intervention. The data partially confirm the intervention's contribution to V‐AMC development. Implications for future interventions targeting competence development are discussed.