Answer:
It varies by state, school system, area you wish to teach, and grade you wish to teach.
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For starters, it's almost always required to take a "Effective Teaching Training" course, and receive that certificate. Also most educational institutes requires a bachelors in education, and or a bachelors in a field of expertise in order to teach. Some educational institutes will allow a teaching position, if the person has an Associate degree, and is working towards a Bachelors degree. Experience is always a plus, become a volunteer because it will look nice on any resume'.