This Data Point examines the supplemental school year income earned at jobs outside the school system by public school teachers in the United States. It uses data from the public school teacher survey of the 2017-18 National Teacher and Principal Survey (NTPS), which is a national sample survey of public and private K-12 schools, principals, and teachers in the 50 states and the District of Columbia. State representative information is also available for public schools, principals, and teachers.