The distinctive characteristic of the initiation model is the principle of recruitment into the class system, a principle based on postpubertal initiation. Where post-pubertal initiation is practiced, children and adolescents have no social autonomy before initiation; after initiation, they are recognized as adults and thus autonomous, in a position to assume socially responsible activities. This social effect of initiation is common to all postpubertal types of initiations. What is characteristic and distinctive of the initiation model is that the undergoing of initiation places the individual in the age class system. Attainment of social autonomy occurs not simply as a result of the initiation, but through the individual's insertion into the aggregation process (the age class) and the promotion process (the age grades), processes unique to age class systems.

In joining a class, individuals acquire a social identification that, in the initiation model, is connected with the idea of age, or the time factor, defined by the time at which they undergo initiation. Therefore, although initiation provides the basis for recruitment into a class, it is the time factor that serves to group the initiates: They will be considered coevals because they have passed through initiation during the same time and are therefore ascribed a common social age. It is this characteristic that defines age classes and distinguishes them from any other type of social class.