A study method that involves covertly or overtly watching subjects’ behaviors in their natural environment, without intervention. Naturalistic observation is a common research method in behavioral sciences such as sociology and psychology.
This technique is great because the experts can see the subject’s behavior in their own natural settings, but one major disadvantage is the fact that it is not always crystal clear what causes certain reactions when you are dealing with so many variables.
Example: A graduate student interested in child development receives permission to observe fifth-grade students through a one-way mirror during class time.
This link talks about the moral implications of observing someone without their consent. It is very interesting: http://www.experiment-resources.com/naturalistic-observation.html