Metacognition seems to have a great influence on modelling processes and the development of modelling competencies. In contrast to the assumed importance, a relatively small number of studies have been conducted so far, as metacognition is a rather complex concept and the measurement of students’ usage of metacognition is rather challenging. As part of the project, the use of metacognitive strategies when working on modelling tasks, as well as students' attitudes towards using them, were measured and evaluated using self-assessment questionnaires and interviews in form of stimulated recalls. In this paper, the outcome of the different methods will be compared and complemented by the analysis of the videotaped working process as a third data source. For this purpose, the self-assessments regarding the use of metacognitive strategies as well as statements in the interview of two students are considered as examples. Conclusions about the different methods and outcomes will be drawn.