This is a well researched fact. The flat structure without a leader normally leads to a official goal of the group (finishing the task) and an unspoken unofficial goal that the unofficial leader is setting by example and retoric.
Everyone needs someone to follow on a team, someone who sets the standard, leads the way and defend the team - even in the most flat structured companies I have encountered this has been true.
If you want a methodology/way to run the team as fair and autonomous as possible, read Daniel Pink's book Drive - it explains what is needed to make people happy in their work.
If you do not want to figure your method out by yourself, steal my method called TimeBlock, it empowers the employees and gives them Purpose, Autonomy and Mastery (ping me if you want one on one help with it)