People who oppose the teaching of evolution in schools often refer to the fact that evolution is technically a theory. It is important to understand the definition of "theory". In science, the word "theory" has a completely different meaning that in other contexts.
Scientific Theory: A DefinitionEdit
"A well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses" (NCSE, 2008).
In science, a theory summarizes a hypothesis or group of hypotheses. In order to reach "theory" status, these hypotheses must be tested and re-tested using the scientific method. Once a concept or idea is considered a theory in the scientific method, it is accepted as a valid explanation for the phenomenon in question (Zimmerman, 2012).
The work of science is never really complete, so different aspects of theories continue to be tested and tweaked. "Theory" is a step in the scientific method, but a concept only reaches this stage after testing and re-testing of several hypotheses, with the results supporting it.
National Center for Science Education (NCSE). (2008). Definitions of fact theory, and law in scientific work. Retrieved on November 26, 2013 from: http://ncse.com/evolution/education/definitions-fact-theory-law
Zimmerman, K. A. (2012). What is a scientific theory? Live Science. Retrieved November 29, 2013 from: http://www.livescience.com/21491-what-is-a-scientific-theory-definition-of-theory.html