In some school districts, teachers are paid in 12 monthly installments, even if the teachers only work for nine months. These districts set aside "deferred income" from the nine months of work to ensure the teachers receive payments during the summer.
Not all school districts defer income; some pay salaries over nine months. Others make salary deferral an option for teachers. Some teachers do extra activities in the summer to earn additional income beyond the nine-month contract. Summer school is one way teachers earn extra money over the summer, while some teachers work temporary jobs to supplement their annual incomes.