Use the attached Quick Reference Card to help you Co-Author Items in Schoolnet. For individual co-authored items, a user with no special Assessment Admin permissions, can only share the item out to their personal item bank. They cannot share it out to others. The user would need a Role that contained the "Create and edit test items for an institution" Operation in order to do this.
Co-authored folders should be created by a highly permissioned user with access to the appropriate item banks. Dring the creation process, this user can specify which "ITEM Central Sharing Rights" should be applied to the folder. Any user with rights to this co-authoring folder will then be able to share out the item depending on the folder settings. When this is setup the SchoolNet Application will ignore the actual or individual rights of the co-author.
Also, attached is additional information on co-authoring from Pearson.