If you’re trying to raise up church planters, pastors, missionaries, or almost any other type of Christian leader, 80% of what you need them to be able to do can be developed in the context of starting and multiplying missional communities. Certain additional skills, such as preaching, would need to be learned elsewhere, but consider all that can be learned in the context of a missional community: shepherding, teaching, evangelism, equipping, hearing from God, sending out, serving. Missional communities are the perfect environment for developing most of these essential leadership skills.
The development of leaders happens best in a real life ministry context. Typically those are churches, but sometimes parachurches, small groups, youth groups, or missional communities function this way. In the broadest sense: any community of Jesus followers living together on mission. No matter what your context is, it needs to be life-related: engaging culture, functioning as Jesus followers in community on mission together. That’s the best environment for raising up the kind of new leaders that we need.