A substitute teacher is a trained, certified, and background-checked education professional who teaches in place of another teacher who is unable to work on a particular day or for a duration of time. Substitutes are often needed in cases of illness, medical leave, or family emergencies. Substitute teachers follow the lesson plan and use supplies, education materials, and teacher-created materials left by the regular teacher. Substitute teachers are tasked with maintaining order and student productivity with as little disruption as possible.