As a PE instructor I believe that kids learn better when they are given the time to be creative and use their imaginations. I do not referee games nor do I keep score. I teach kids the importance of good sportsmanship and teamwork. We play to have fun not to win or lose. I feel that when kids have the freedom to explore their skills, they are better able to figure out their strengths and weaknesses.
At the elementary level it is too early to specialize kids in positions on teams. All kids develop differently. They need to explore all skills and all positions to find out what they like and what they are strong in. If they are constantly being told what to do and how to do it they become resentful and bored.