Depends on the co-op.
I lived in a student co-op in college. Every Sunday night we had a group meeting. Every major decision was made by a consensus making process. Other decisions were delegated to committees or individuals in a particular position: food manager, garden manager etc.
I also worked at a student composting/waste disposal co-op that operated the same. Everyone has a voice in either the actual decision or in electing someone to make a decision.
This type of decision making basically requires lots of communication between members and usually at least one long meeting a week. It also demands that people have mutual respect for each other and the group decision making process.
In both instances it definitely helped me learn to relate with, communicate with and respect others and their opinions.