Hart and Risley have developed an incidental teaching method to teach the spontaneous use of functional language for mildly language-delayed children within natural environments. Their method appeared advantageous, because it incorporates language into robust, behavioral-like chains already functional in a natural setting. The method in larger population, however, is quite unexplored, especially with severely language-deficient persons, not having large functional behavioral repertoires. The present paper analyzes the incidental-teaching method and its prerequisites, and offers systematic ways to apply this method to more severely language-deficient children. In addition this paper is an attempt to make an extended teaching method of functional language by putting in perspective ecobehavioral analysis of natural environments.