There is a tendency to use case-study research methodology for research issues aiming at simply describing a complex situation, and to draw conclusions with insufficient rigour. Sound case-study research, however, follows discriminate rules which can be described in all the dimensions of a full case-study research process. This paper examines dimensions of case-study research methodology, relating them to scientific research quality criteria. The reasoning is illustrated by the example of case-study research which has been conducted on issues of sustainable development in secondary and higher education. The process of data collection and interpretation and the procedure of drawing evidence from the outcomes are shown, leading to conclusions about quality criteria in case-study research.