I'm working with a pastor whose church has 60% of their members in groups. His desire, which is typical for most pastors I work with, is to see 100% in groups and for those groups to be far more missional and transformational than they are today.
However, he (and more importantly his staff and leadership team) doesn't seem to understand that for this to take place, group life must not compete with the other programs in the church, be seen as one of many for involvement, or perceived as a supportive program for the pulpit or weekend services.
Right now, the youth pastor and children's pastor are cherry picking the small groups for volunteers in their areas and effectively robbing the groups of future leaders, not to mention that their areas require so much involvement that the people they pull from the small groups really have no time to be a part of a small group as an arm's length member.
You can't have it both ways. It's crazy thinking to push small group life from the pulpit when it's not the missional thrust of your church and without a clear understanding that it's too time consuming to compete with other programs.
When a church (not just the pastor) makes a life-changing decision to become missional group life driven, everything must change. In fact, job descriptions must be re-written so staff members don't act like car salesmen on the floor of a sparsely populated sales floor. In healthy group-driven churches, the youth ministry and children's ministry supports the small group ministry because the groups are fulfilling the mission. Youth small groups are launched. The children's ministry pastor must start thinking of how to integrate children into group life, not just the razzle dazzle on weekends. And everyone must work toward making small groups the main thing so the members understand that they are the church, not programs operating inside a building on a campus somewhere.
As far as transitions go, this is one of the greatest challenges a church goes through to help the old school program driven mindsets change.