Police officers were not always in schools. When the concept of having a police officer solely stationed in a school emerged in the 1950s, there were fewer than 100 police officers working on American school grounds.
The role of school police officers remained fairly limited for the following decades, with an emphasis on event security and parking lot management. But the tough-on-crime political culture of the 1980s led to an increase in the number of school police officers.
With the popularization of racist narratives of "juvenile super-predators," school police officers became an increasingly common presence, particularly in urban schools. Further, the Gun Free School Zone Act of 1994, which required that a student be expelled for a minimum of one year if he or she brought a gun to school, created the perceived need to have police officers on school grounds so they could enforce this law.
Additionally, during the late 1990s and early 2000s a series of highly publicized incidents of school violence increased the number of police officers present in schools. It is important to note that these reactions were not based on research and data about what actually improves school safety, but were reactionary and rooted in fear.