"Each day, about 5 million children walk into 274,000 classrooms nationwide and find a substitute. Students today will spend at least one full year with a substitute by the time they graduate from high school -- a figure that's higher in poor schools and destined to increase." The situation today has worsened. It is estimated that more than 300,000 classrooms and over 5.5 million students are taught by substitute teachers each day in the United States. In between jobs, haven't found the job you are best qualified for, don't like rigid structured work schedules, or retired and looking for some part time work? Substitute teaching maybe just right for you. Substitute teachers, Subs, or as they are sometimes called guest teachers simply put, teach students in a public or private school when the, or a regular teacher is unavailable.