Some parents may withdraw support for economic reasons -- primarily the concern the school is spending too much and costing them too much in tax dollars. Schools usually must pass budgets in their towns or cities and if parents are displeased with cost increases, they could urge their council members of board of supervisors to vote down the budget.
Contrarily, some parents feel the schools are not investing enough money into their schools. Some parents are willing to pay more in taxes to ensure smaller classrooms, quality food, foreign language courses, music and physical education equipment. If school boards don't spend enough to maintain quality services for students, parents may not support the schools.
Many political and religious aspects of school can force parents to withdraw support. For example, some parents feel schools should teach evolution as well as religious explanations for the origin of man in science classes, while others vehemently oppose such a curriculum. Other parents want prayer in school, while others are deeply opposed. These political and cultural aspects can cause parents to withdraw support for schools.
Parents are often concerned about safety at school. If schools do not have safe playgrounds, background checks on teachers, enough adult supervision or methods for dealing with bullying, frustrated parents may withdraw support for the school. This is especially true if there is a history of violence or abuse at the institution.