Email. I am sold on email.
I manage the backstage volunteer effort at my rink for the ice shows. We do two ice shows a year, including an all-out Nutcracker on Ice with a couple of hundred skaters in 15 groups, and 85 soloists/duets/trios (sharing parts). The coaches manage and direct the show, but all the off-ice traffic, kid wrangling, security and costumes are handled by parent volunteers.
We had 70 people working these areas over the four days of the run, and they were the best volunteer crew I ever had. And I owe it all to email.
I've written before about the importance of communication; the more pertinent information you share, the better your experience will be. Better information means less drama because people get uncomfortable when they don't know what's going on. Because all the coaches now have park district email accounts, I was able to send emails first to every parent in the show asking for volunteers, and then to communicate easily with those who signed up. Everyone got pre-show emails to make sure they knew where they were supposed to be, when they were supposed to be there, and what they were supposed to do once there.
First, every parent knew that there were volunteers in charge, because they had all gotten an email asking for help. Even though most chose not to volunteer, everyone had gotten a direct communication dedicated to the subject, rather than just a passive "sign up" request with the show packet. The most critical question that every ice show parent has when they see the chaos that is 220 children backstage, is "who is watching my child." Because of the good communication effort this time, everyone knew that there was someone watching.
Second, the volunteers knew what they would find, and what they should do before they ever walked through the door. To the uninitiated, an ice rink can tend to seem like a mysterious society with arcane rules and impenetrable power structures (it certainly seems that way to me, and I've been living in one since 1992). Open communication bares the mystery: what does a volunteer do? I was able to let them know upfront that they really didn't need to know anything about skating-- that's our job. They were there to watch the kids, something they all know how to do.
Any public enterprise--be it a business, a school, a place of worship, or an ice rink--has proprietary information. There are things management knows that staff does not need to know, and there are things that staff needs to know that customers don't need to know. But it's important to make that distinction, and to let people know what they need to know. It's also important not to assume that people know more than they do, and to identify information that will increase both their buy-in and their comfort level. If you want to have any sort of control over your program, don't control the information by withholding it-- people will just make up shit if you do that (pardon me, it was really the best way to put it). Control the information by sharing it.
And just in case I haven't said it enough: thank you volunteers. You made my job easy.
Another great article on volunteers over at IceMom!