In this empirical study it was hypothesized that visible diversity and education level (diversity) are positively related to cognitive diversity and critical reflective work behaviour. But that in order to harvest the benefits of diversity, beliefs of valuing diversity are needed. Gender diversity and the average level of education within a team are found to increase the level of cognitive diversity. Analyses further revealed significant effects of task complexity and sector influences regarding critical reflective work behaviour. However, cognitive diversity did not resulted in more critical reflective work behaviour within teams. Therefore the moderating role of diversity beliefs could not be examined. The promise of diversity could not be demonstrated and more research is needed to provide more insight in the reality of diversity. Future recommendations are made and practical implications for organisations are given.