The average family size around the world is seven people, plus or minus two. The optimal team size is seven people, plus or minus two. Google’s new facilities in Switzerland and Ireland are filled not only with wide-open spaces, but with rooms with eight desks in them. Coincidence?

Not likely. The anthropological research across cultures indicates that groups of seven people, plus or minus two, create the strongest trust bonds and best reinforce cultural norms.

I recently wrote an article for Forbes on the value of a nested approach to office layouts. The main points of that article are that people should:

• Pay attention to their team’s physical environment. It’s one of the five fundamental planks of culture.

• Be careful of the unintended consequences of completely open plan, flexible offices. They’ll certainly save money. But at what cost in terms of trust, reinforcement of cultural norms, and feelings of security?

• Physically nest teams of six to eight from the larger extended group/family of 24 and in tribes of 150.

These insights are applicable to training and development as well and particularly to a discussion about the ideal class size for training. There are obvious advantages to one-on-one training with regards to such issues as intimacy, customization, and so forth.

There are obvious scale advantages to training in larger groups. While there are always going to be situations where going small or going large makes sense, if you follow the implications of the anthropological research, you should bias your training to groups of six to eight.

Training in groups that are too small

The argument against groups of less than five people is that participants will miss out on the benefits of diverse thinking. Training classes of four or less people may resemble simultaneous one-on-one learning more than they look like group learning.

The primary interactions are between teacher and learner, not between group members. The learners learn from the teacher, not from each other. This is, of course, wonderful if the teacher is good. It’s less wonderful if the teacher is not so good.

In most of my learning experiences after high school I learned far more from my fellow students than from the teachers.

Training in groups that are too big

The argument against classes of more than nine people is that they default to lectures. The ability of any individual to hide in the class increases with the size of the class. You don’t want people to hide. You want them to engage with the material and with each other. Too big is too bad.

Training in groups that are just the right size

Groups of six to eight people are large enough to have diversity of thought and small enough to encourage and enable engagement. Learners can interact with the material, the teacher and with each other. They can get to know each other. They can learn to trust each other.

Implications for trainers

Pay attention to the physical environment of your training and development. Be careful of the unintended consequences of completely open plan, flexible training. It may save you money, but at what cost in terms of trust-building and content mastery?

Bottom line: It’s best to have a bias to nest your training in groups of six to eight learners.