title_body: Is there a constructed language in existence that has graduated to "natural" status? That is, are there any such languages in use today that are in use for day to day activities, or are formally recognized, etc?
upvoted_answer: For varying definitions of "conlang", yes:
  
  
  The very most obvious example is Esperanto with a well-documented native speaker community. It has received limited official recognition, the most interesting of which currently seems to be PR of China's El Popola Ĉinio magazine and China Radio International in Esperanto. There are many more.
  A less obvious example would be Classical Sanskrit, which was, arguably, constructed by Pāṇini, and is a Scheduled Language of India with some fifty thousand people speaking it in 1991; it is furthermore an official language of the Indian state of Uttarakhand, and reportedly the language of the majority in a village called Mathoor. It is used across all levels of education across India.
  A more controversial example would be Modern Hebrew, one of the few successfully revived language in modern times. The page on Wikipedia gives a solid overview of the situation, and is fairly unbiased. Of the three mentioned here, Hebrew is arguably the most successful "graduated" language — if you consider it a conlang to begin with.