Schooling is particularly characteristic among many of the Odontocetes,
schools of some dolphins habitually contain hundreds and sometimes thousands of animals.
In Cetaceans the schooling habit may well be due to the monotonous character of the environment, for the upper waters of the oceans do not show any topographical differences so that it is practically featureless away from the neighborhood of the coastlines.
For the purpose of reproduction, it is essential for animals to be able to find each other at the appropriate season, and the schooling habit obviously facilitates this.  
The limited range of visibility underwater may also tend to encourage schooling by keeping the animals within sight of each other.
Cetaceans, either in schools or as isolated individuals, are probably acoustically aware of the presence and relative positions of others in a very large area of the ocean surrounding them.

Within the social group there is a well defined dominance order. Mature males are all generally dominant over all females. Among each sex there is also a fairly well defined order. This has been observed in captive groups, but scars and spasmodic observations in nature suggest that similar  hierarchies exists in the wild. There seems to be considerable social responsibility among a natural group. On several occasions school mates have been observed in close proximity to, and even psychically assisting, injured colleagues. The dominant animals swim above nearest the surface, and the subordinate ones below.
It has been suggested that the interface between water and air is the most important feature of the environment for all cetaceans, for and consequently the upper layer in a school is the best place and is the one therefore occupied by the dominant animals.

When different groups meet, they are stimulated to unusually lively social interactions, they 'leaped', performed airborne cartwheels and chased, rubbed against, mouthed, and struck each other with the flukes. These actions resemble the normal sexual or 'courtship' display, and apparently acted also as 'greetings' ceremony, which may well reinforce social bonds when the members of a school unite.