In the present paper, the development and use of a specific set of pedagogical design principles in a large research and development project are analysed. The project (the Knowledge Practices Laboratory) developed technology and a pedagogical approach to support certain kinds of collaborative knowledge creation practices related to the "trialogical" approach on learning. The design principles for trialogical learning are examined from three main developmental perspectives that were emphasised in the project: theory, pedagogy, and technology. As expected, the design principles had many different roles but not as straightforward or overarching as was planned. In their outer form they were more resistant to big changes than was expected but they were elaborated and specified during the process. How theories change in design-based research is discussed on the basis of the analysis. Design principles are usually seen as providing a bridge between theory and practice, but the present case showed that also complementary, more concrete frameworks are needed for bridging theory to practical pedagogical or technical design solutions. (Contains 2 figures and 1 note.)