For our school we use the Mantra Theme :
The pupils can write posts together and I order that they can work separetly on the same text we use the plugin "Co-Authors Plus".
But, the template has to be modified (as like replacing tags like the_authors() ) in order to show the other authors.
There is explanations here : http://vip.wordpress.com/documentation/incorporate-co-authors-plus-template-tags-into-your-theme/
So where can I find the tags the_author() and the_author_posts_link().
Thanks for your help.