Indeed, school exclusion, without these supports, can exacerbate a bad situation. In the Parkland case, the fact that Nikolas Cruz had been expelled from school may have contributed to driving an angry young man who felt isolated to take out his frustration and anger by killing students and staff at his former school. In theory, zero-tolerance policies deter students from violent or illegal behavior because the punishment for such a violation is harsh and certain. However, research shows that such policies ultimately increase illegal behavior and have negative effects on student academic achievement, attainment, welfare, and school culture.