Small groups are biblically grounded in Jesus' gathering of a group around him for the purpose of discipleship. See Allan Coppedge's book, "The Biblical Principles of Discipleship" (FAP/Zondervan, 1989).

Well I'm not sure if they guy needs to abandon Roger (or who the heck he is for that matter), but small groups can be very biblical. His friends may have a valid criticism that they sometimes turn in to group therapy, but thats not intrinsic to a small group. They (his friends) need to get off their regulative principle steroids!

Meeting together to pray, study the Scriptures, encourage one another... who would discourage that?

I’ve heard this type of comment before in Reformed circles. But I’ve also seen Reformed (PCA) churhes trade adult Sunday School for small groups.
Now Sunday School is not in the Bible either - but I’m curious about thoughts on trading Small Groups for Adult Sunday School.

In historical perspective, while perhaps there is not a 1:1 correspondence, still there were many kinds of 'small groups' during the Reformation, Second Reformation, and beyond. The Scottish Presbyterians had their conventicles, the Dutch Reformed their gezelschappen, etc. I believe Edwards encouraged prayer meetings of all sorts, even countenancing those initiated and led by children!

On a biblical note, the saints in Jerusalem met in the temple daily as well as in house gatherings. What exactly these looked like, I'm not sure. Classic Presbyterianism has tended to view them as full blown churches, but I'm not so sure. Even so, you clearly have the massive gatherings of Acts 6 as well as the smaller gatherings throughout the various wards in private homes.

If this duplicates something written before, sorry. I just clicked in.

Another important biblical basis for small groups is the litany of "one another" texts, such as:

Bear with one another (Ephesians 4:2)
Forgive one another (Colossians 3:13)
Confess your sins to one another (James 5:16)
Pray for one another (James 5:16)
Show hospitality to one another (1 Peter 4:9)
Accept one another (Romans 15:7)
Be subject to one another (Ephesians 5:21)
Encourage one another (1 Thessalonians 4:18)
Admonish one another (Colossians 3:16)
Stir one another up (Hebrews 10:24)
Be kind to one another (Ephesians 4:32)
Honor one another (Romans 12:10)
Bear one another’s burdens (Galatians 6:2)
Love one another (Romans 13:8)

In order to practice the reciprocal ministry actions called for in these passages, believers need to be involved in groups/fellowships small enough to allow for such give and take. To put it the other way around, it's impossible to live out the back-and-forth of "one another" in the large gathering--we just can't know others and be known in ways that match the depth of relationship called for in these texts without small groups.

I recommend reading "Why Small Groups?" by C.J. Mahaney and the guys at Sovereign Grace. I would also recommend "Life Together" by Dietrich Bonhoeffer.

Small Groups...lets say 3 to 15 believers...are certainly biblical. (side note: most church plants in persecuted countries are no more than 10 to 12) The reader is actually right on in the comment that small groups provide a place for the "non-pastor" to disciple believers. Its also a place where the church can live out Acts 2.

The above comments do a good job and I hate writing long comments so That's all I got. For more on small group philosophy & ministry check out my blog!

One thing I would add is to be careful of the composition of small groups. I'm not completely sold on the idea of making them homogenous. I support smalls groups that are mixed in age and mixed in stage of life. For the reasons stated in Titus 2, it makes sense to me to have old and young together in small groups.

Titus 2:1-7 “But as for you, speak the things which are fitting for sound doctrine. Older men are to be temperate, dignified, sensible, sound in faith, in love, in perseverance. Older women likewise are to be reverent in their behavior, not malicious gossips, nor enslaved to much wine, teaching what is good, that they may encourage the young women to love their husbands, to love their children, to be sensible, pure, workers at home, kind, being subject to their own husbands, that the word of God may not be dishonored. Likewise urge the young men to be sensible; in all things show yourself to be an example of good deeds, wit, purity in doctrine, dignified.”