It is my firm belief that anyone can teach! Everyone has something to share even if it’s what NOT to do and therefore anyone can teach. But I think the bigger question here is what makes a teacher effective, because every teacher is not effective. In that sense a person should have the education, experience, and expertise to share their subject knowledge with another. They should have a thourough understanding of how learners learn, content, information process, and assessments. They should have full knowledge of the education process which can happen in a degreed program or certification program. To answer your question a person can be qualified by being gifted in this area or developing the talent through education, experience, and expertise. 

The most important characteristic of a teacher is tenacity. There are so many types of learners and learning environment that the teacher will encounter through his or her tenure. The ability to hold it together and persevere despite challenges makes the tenacious teacher effective. The tenacious teacher is willing to try various strategies and methods to reach the struggling learner and wants wholeheartedly to see them succeed and reach their goals. Tenacity allows the teacher to study and learn their subject matter in and out. Without this characteristic I don’t think teachers would exist!