This article has been footnoted and quoted in many books and articles since. Schaller presents four numerical barrier when people assemble. Each of these four group takes different leadership techniques and has different leadership demands. Quite frequently the size of the classroom, chairs, and table arrangement dictates the upper limits to a group in spite of what leadership does. In general, whenever human beings gather in a voluntary association that emphasizes relationships with one another, there is a natural tendency to limit the size to fewer than 40 persons.
Illustrations are numerous.
Throughout history, all military organizations have limited the basic unit to fewer than 40. Major league baseball teams limit a team' s roster to 40 in the winter and 25 after the season begins. The Lion's Club that wins the regional attendance award usually has fewer than 40 members. One-fourth of all Protestant congregations in North America average fewer than 35 in Sunday worship. Very few adult Sunday school classes, regardless of their enrollment, average more than 40 in attendance.