Abstract
The research presented in this paper focuses on the cognitive diagnostic strategies that prospective elementary mathematics teachers (PTs) use in their reflections of one-on-one diagnostic interviews with children in grade one. Thereby, it responds to the detected lack of knowledge regarding qualitative facets of diagnostic proceeding in interview assessments. Results include facets of collecting data and facets of interpreting within a diagnostic micro-process. The discussion takes up the relevance of these findings for teacher education.