In the 1700's John Wesley resurrected the model of the smaller Christian groups. To supplement the normal Anglican church service, he organized the people converted under his ministry into "society" groups They met weekly for fellowship, preaching, prayer and hymn-singing. Members agreed to follow three general rules: Avoid evil, do good and employ the means of grace God gives for spiritual growth. The three earmarks of the Methodists were tireless evangelism, emphasis on discipleship and a spirit of charity.
The society groups could be divided into smaller groups called "classes" that would provide for even more intimate spiritual support and nurture. These classes were composed of about a dozen people who met once a week for spiritual conversation and guidance. Members spoke about their temptations, confessed their faults, shared their concerns, testified to the working of God in their lives and exhorted & prayed for each other. Every Methodist was expected to attend class meetings. Attendance was a requirement for admission to some other gatherings.
If a believer was dismissed from the society for some reason, entrance back into the society was made possible through participation in a “penitent band.” These bands were designed to aid the believer through intimate fellowship and strict discipline. This kind of group was made up of 4 to 6 people with intense accountability.
John Wesley's social structure combined with great zeal was close enough to the New Testament church that it was very fruitful in leavening the societies of England and America. The need for personal conversion, prayer, and Bible study may seem so obvious within the evangelical community as to barely merit mentioning. The uncomfortable reality, however, is that many contemporary evangelicals and their preachers don’t pray and feed upon the Word daily. Such passivity all too often leads to gracelessness and an impotent witness. In contrast, Wesley knew that God’s grace has to be cultivated with active faith. Miss this, miss reformation.
There are brethren who consider John Wesley to be the father of the small group movement of today. See this link.