To encourage students to do geometry, the art of Islamic geometric ornamentation was chosen as the central theme of a lesson strand which was developed using the newly presented didactical tool called 'Learning by Acting'. The Dutch students who took these lessons in 2010 to 2013 were challenged to act as if they themselves were Persian medieval designers of geometric patterns and construct new mosaics. Their presentations proved that they were proud of their results and gained Mathematical knowledge. The teachers welcomed the new didactical approach. As a side-effect, it improves cultural awareness among students from various religious backgrounds.