Small groups—in which 6 to 12 people regularly gather to talk about their spiritual journeys, study the Bible, and pray—have become an integral and dynamic part of modern American church life. They have helped transform thousands of churches and millions of individuals. Though many think they were invented in the last couple of decades, they've been around in one form or another since the early 1700s, with the ministry of Methodist founders John and Charles Wesley.

June marked the 300th anniversary of John Wesley's birth, and Christianity Today took the occasion to look at one of Wesley's most enduring legacies. To explore the Wesleys' small-group innovations—and what they might teach us today—we asked senior writer Tim Stafford to talk with Tom Albin, dean of The Upper Room in Nashville. Albin did doctoral research at Cambridge University on the small groups of early Methodism, and he helps lead one of the most significant renewal groups in Methodism.

Why do historians often call the Wesley brothers organizational geniuses?

They often say that the secret of the Methodist movement was its small groups. But when I began my research, I found that nobody had gone deeply into what made those small group structures work. In the 18th century, the Wesleys were remarkably effective within the oral tradition of a working class, almost semiliterate culture. There were no manuals for class leaders produced during the lifetime of the Wesleys. To answer the question, you had to look to letters and diaries for clues.

So what were the early groups like?

There was a rich diversity of groups that emerged within the first five years. The trial band, for example, distinguished a sincere seeker for God from somebody who was just casually curious. ...