A South Carolina head resigned amid public pressure last week after sanctioning a commando-style police raid in which officers stormed classes, guns drawn, handcuffing and pinning students to the floor in a futile drugs search.
As well as encouraging heavy-handed methods, critics say the approach fails to distinguish between idle fantasy and real violence, aspirins and illicit drugs, or pen-knifes and guns.
Heads returning after Christmas to schools in Louisiana last week were ordered not to expel students for possession of over-the-counter medicine.
Last term a girl was barred for carrying headache pills. School officials upheld the 15-year-old's expulsion, however, along with that of another student found with an antihistamine tablet.
In October, 2003 Nobel literature laureate JM Coetzee petitioned California's Supreme Court, contending that the violent poetry that led to a Silicon Valley teenager's expulsion from school and three-month incarceration was harmless self-expression.
Utah lawmakers plan to sponsor a state bill later this month that would modify a blanket drug ban in schools there, permitting students with a doctor's note to carry asthma inhalers. A Texas pupil was suspended and arrested under a similar policy last September, after passing his inhaler to a classmate who was having an attack.
Higher suspension rates are associated with higher dropout and juvenile delinquency incidences, according to a Harvard university study.
Zero tolerance often deprives teachers of discretion in administering punishment, said Delbert Elliott, director of the University of Colorado's centre for the study and prevention of violence.
It dates back to Reagan-era drug policies in many cases, but a spate of deadly school shootings, including the 1999 Columbine massacre, have given it fresh impetus.
David Vodila, headteacher of Pennsylvania's Red Lion high school, understands better than most the high stakes of violence in America. Last April, his "good friend", the principal of neighbouring Red Lion junior high, was shot dead by a pupil, who then turned the gun on himself.
Mr Vodila doubted whether zero tolerance, in place at Red Lion juniors, deters students bent on serious crime. "The rule won't make a bit of difference if you're dealing with an insane act as we did - it didn't mean anything to the young man who did that terrible deed."
By contrast, Mr Vodila intervened recently to ensure an outstanding student who worked after school at a florist was not expelled for carrying a flower knife.