This study reports on the development and usefulness of an assessment procedure for teachers' coaching competence. We examined the usefulness of the developed procedure with respect to making reliable judgments. Video portfolios were constructed by researchers, which consisted of deliberately planned video recordings of teachers' coaching performance in the classroom and additional data sources providing context information. Six trained assessors scored three video portfolios. Interrater agreement was determined and assessors were interviewed. Judgments across assessors were relatively similar. Both supportive and hindering aspects in the procedure for making reliable judgments could be derived from the interviews. Theoretical insights about assessor scoring are discussed, and implications for optimizing the assessment procedure are described. (Contains 6 tables.)