Call them small groups or call them Sunday School classes. Churches differ on what they call these and how they structure them. We have a Sunday School time at 9AM, but some of our classes structure themselves as a small group hybrid model. They engage in out-of-class time fellowship activities and share life together. We have groups/classess for all ages to help Christians grow in their knowledge and faithfulness to the Lord.
We aim to honor Jesus' charge that the church's mission is to make disciples. Once people come to faith in Christ and are baptized into His church, it is the church's job to "teach them all I (Christ) have commanded them" (Matthew 28:20a).
These classes/groups are our church's way of engaging in life-long discipleship for followers of Jesus.