Reading some article about how to get children to be more sociable, especially the shy ones, I remembered the magical two words about a very good method the help them integrate into a collectivity: sports & team. All that articles I've read in the last hours where considering that the shy kid was the only child in the family and he was surrounded by adults, with other children somewhere in the background.
I practice a sport constantly and it's already a decade since I've started, so I experienced the bound that is forming between people, the younger they are the more powerful is the bound. They were always saying that sport (in general) is an activity that develop the mind and the body of a human being, but it's much more than that: it can help improving his/her social life. In some cases practicing a sport can make somebody popular or famous, but it's sure that the practice will make him more sociable. Sports are having the magical quality to take the shy away from the expression “shy kid”, but it takes some time to happen.
Convincing a child to constantly move according to some rules it can only make him react to some clearly defined stimuli, acknowledging the results he is getting through his own actions will only increase the trust in himself. Team sports will make children depend of one another (in some degrees) and to make connection that help building the team.
A shy child is a kid with no (enough) trust in himself and no connections to other children. Of course you have to treat him different than others: do not shout at him, do not pull him into the stressful situation, allow to feel himself and try to make him confident in himself and what he can do. It's not easy, it takes patience, energy and some time (usually longer the some would like), but a team sport will only help you in your work as parent. A good sport teacher will understand the problems with a shy kid, so try to maintain a good relation and a better communication with him.
As a parent is difficult to pay attention all the time to your child, especially when he is training away from you, with other children, but ask him as often as you can about the sport activities. Children love to brag about their success “we did that”, “we won the cup”, “in the trip we were swimming” (and a lot of other stuff), “we were camping and made a fire”. Encouraging a kid to express himself will only show him he can gain some other people's respect by his actions and his team actions.