School security encompasses all measures taken to combat threats to people and property in education environments. One term connected to school security is school safety, which is defined as the sheltering of students from violence and bullying, as well as exposure to harmful elements such as drugs, guns and gang activity. Along with other public places, schools are at risk for invasion from outside as well as attacks from students or faculty because of the high traffic of potential assailants and availability of victims.

In the US, as of January 2018, since 1990, at least 240 school shootings have occurred. School shootings have a 450% increase in the past 30 years, in which there were only 53 shootings. School bombings are less frequent at 22 in 2016, but according to the US Bomb Data Center, education related buildings are over twice as threatened than any other target. Over 74% of education related threats were middle schools, junior high, and high schools. Due to safety threats, during the 2013–2014 school year, reports say 93% of public schools lock or monitor doors and gates as a means of controlling access to the school; this is an 18% increase since the turn of the century.

Metal detectors are installed at the entrances of a small number of US schools to deter students from bringing metal weapons into schools. As of 2022^[update], 2.4% of US schools had students go through metal detectors every day, and an additional 6.2% of schools sometimes used metal detectors for random checks.

Vandalism is often a problem for schools as they are an easy target. What constitutes vandalism varies among reports, which makes it difficult to get an accurate view of the extent of vandalism. However, vandalism generally refers to damage to property (graffiti, etc.) and break-ins. The Center for Problem Oriented Policing categorizes break-ins as being of three types: nuisance break-ins, where a break-in is done just for the sake of it; professional break-ins, with an intent of theft; and malicious break-ins, where damage is caused out of spite. Solutions for preventing vandalism include providing after-school and evening programs to engage youth that are loitering, improving lighting, adding security patrols, and education for students on anti-vandalism.

The New Zealand government provides funding to public schools to repair vandalism. This funding comes from different sources depending on the type of damage that occurs. Two important guidelines regarding vandalism repair are that it must "be carried out immediately, and comply with Ministry standards."

The National Center for Education Statistics reports that in the U.S., 20.8% of students ages 12–18 experienced bullying at school in 2014–15. Prevention for bullying by parents, teachers, and other adults includes talking to students about bullying, modeling treating others with kindness, and helping students get involved in something they are passionate about. Helping students understand the importance of bully reporting and learning ways to stop others from bullying can also be effective.

Between the ages of 11 and 15, in most countries around the world, boys are bullied more than girls. As reported by Young People's Health in Context, in Israel, almost twice as many boys ages 13–15 are bullied than girls; Belgium has a difference nearly as high. On average, bullying tends to peak at age 13. Lithuania experiences the highest level of bullying, with an average of 63.6% for girls between the ages of 11 and 15, and an average of 65% for boys between the ages of 11 and 15. Sweden experiences the lowest level of bullying, with an average of 14.7% for girls between 11 and 15, and an average of 15.3% for boys between 11 and 15.

Prevention methods fall into two main categories: threat assessment and physical measures. Noticing that a student is showing signs of depression or drug use and speaking to the student to learn more is an example of threat assessment. A lockable door is an example of physical measures.