Diverse MBA teams perform worse

From "Diversity and Performance in Entrepreneurial Teams" (SSRN): 

• Among the randomly-assigned teams [of MBA students], greater diversity along the intersection of gender and race/ethnicity significantly reduced performance. 
• However, the negative effect of this diversity is alleviated ... [when teams can choose their teammates]
• ...teams with more female members perform substantially better when their faculty section leader was also female.