Having in mind that the purpose of the task is to check each ones knowlege and skills I find obvious the decision you have to make, because you are not able to correnctly rate theirs skills. However, in order to develop theirs teamwork skills you can assign them group tasks.
Thanks for that, I think what bugs me is that in the midst of fulfilling the objectives to my lesson, I wonder sometimes if certain skills like this have gone unnoticed.