The National School Safety Center has issued this list  of characteristics that teachers and parents should  watch for in students, including:

Characteristically resorts to name calling, cursing or abusive language.

Habitually makes violent threats when angry.

Has previously brought a weapon to school.

Has a background of serious disciplinary problems.

Has a background of drug, alcohol or other substance abuse or dependency.

Has few or no close friends.

Is preoccupied with weapons, explosives or other incendiary devices.

Displays cruelty to animals.

Has witnessed or been a victim of neglect or abuse in the home.

Bullies or intimidates peers or younger children.

Tends to blame others for difficulties and problems they cause.

Consistently prefers TV shows, reading materials, movies or music expressing violent themes, rituals and abuse.

Reflects anger, frustration and the dark side of life in school writing projects.

Is involved with a gang or an antisocial group on the fringe of peer acceptance.

Is often depressed and has significant mood swings.

Has threatened or attempted suicide.

Has tantrums and uncontrollable angry outbursts.

Source: Associated Press