The assessment centre involved an interview, which was based on a questionnaire that you were asked to complete beforehand (my poor performance on that questionnaire led to an unsuccessful interview); it also involved a group exercise, which was relatively straight forward - focus on the teamwork, not having your option win! There was also a test that many people found difficult, but seemed to be based on logic. There was also a presentation on how dcc should expand into a particular country. Ours was Spain, but this changes every year. Use prezi - few people do and it shows a bit of creativity.