If you're going to help servants grow in their leadership, you need to decide what roles are of higher priority than others. For example, here is how this model plays out with our greeters:
Single A volunteer – person greeting on Sunday
Double A volunteer – person overseeing that team of greeters that morning
Triple A volunteer – person who oversees the greeter ministry
Major Leagues – Staff member who oversees our entire hospitality area
The key is to move people as you see the potential in them flourish. I talk about this model in my book Zero to Sixty: 60 principles and practices for leading a growing church. There's nothing worse than a faithful volunteer with huge potential staying at a single A spot.
(FYI – just don't move them until you've seen a level of faithfulness in them that you feel comfortable moving them to the next level). Because the only thing worse than not promoting a faithful volunteer with the potential to do move is to promote an unfaithful volunteer who has not been faithful with his/her God-given gifts.