I suppose I look at it more from a career outcome position than an academic one - in that in most fields you will be working with a mixture of people and the longer you have had to understand and get to know a wide range of people including both sexes prior to starting work the better.
I'm not sure that one can draw a line so sharply between career and academic outcomes
One of the arguments advanced by proponents of all girls schools is that it offers them more leadership roles and encourages them to own the roles properly. Similarly articles I have read argue that girls are more likely lead class discussions so in a boys only environment boys get more adapt at leading conversation rather than just following.