I am a Scoutmaster of a relatively new troop...we are in our third year... and a rookie to the Scouter forums. For the past two years at summer camp our guys have witnessed the callout ceremony. When they have asked questions, we have answered them as best we could. This is the first year we were able to have elections, and two of our guys were elected and called out at camp.
When the election team came to our troop, we did our best to explain to the guys about the OA, its purpose, as well as the character of the young men they were to elect to be a part of it. We made it clear at that time that the OA is not a secret organization and we explained in very basic terms what would be involved in the Ordeal and how the Brotherhood later "sealed" a Scout's membership in the OA. We didn't go into much detail, but just enough to let the guys know what would be expected of them if and when they were elected.
Immediately prior to the call-out ceremony at camp I reminded the guys again about what the OA was about, that they should be happy for whoever would be called out (we didn't tell the guys who was elected). I also reminded everyone, and especially those who were eligible but were not elected, that the OA is about service. Everyone, if they meet the basic requirements can be eligible, but it is only by being recognized by their fellow Scouts as being a competent camper, a leader and a servant, can they be elected.
The call out ceremony was a great experience for our troop at camp (and all the parents who attended). After the ceremony we were able to answer even more questions some of the guys had.
The mystery of the ceremonies and the symbolism of the OA should never--by anyone--be used to scare younger Scouts or to develop some kind of "hierarchy" or class mentality in the troop ("we're in and you're not!"). That undercuts the values and character that the OA stands for.