Terrified by a rash of school shootings around the country over the past few years, most schools in the United States have brought in a tough discipline policy known as "zero tolerance," designed to mercilessly root out guns and drugs. The only problem is that the  rules aren't just being applied to handguns and heroin.

Teachers and school administrators are invoking them in a widening range of minor offences, causing a growing backlash.

Some of the recent cases of zero-tolerance discipline have fueled concern about the policy:

- -Tawana Dawson, 15, a Florida high school student, was expelled for one year for bringing nail clippers to class. The school felt that the two-inch nail cleaning attachment qualified as a weapon. After a legal challenge, she was allowed to return to class under strict probation.

- -Two 10-year-olds in Virginia faced felony charges for putting soap in their teacher's water bottle. The teacher decided to press charges because he thought he was being poisoned.

- -A Texas 13-year-old spent six days behind bars for a Halloween creative writing assignment in which he described a school shooting. The teacher asked for a scary story and gave him an "A" on the assignment before turning him in to the principal.

- -In West Virginia, a seventh grader was suspended for three days for violating his school's anti-drug policy. He shared a zinc cough drop with a classmate.

- -Twenty children have been suspended since 1996 for bringing Alka-Seltzer to school.

The fight against zero tolerance is uniting right-wingers, who fear students' rights are being trampled, with left-wingers, who worry the policies are overly harsh on black students.

Many of the lawsuits against zero tolerance are spearheaded by the Rutherford Institute, the same outfit that helped Paula Jones in her sexual harassment lawsuit against Bill Clinton, the U.S. president.

"It can screw with your life and you're talking about good people, and students," said John Whitehead, president of the institute.

The most visible challenge to zero tolerance is being led by black civil rights leader Jesse Jackson, who is fighting the expulsion of six black students in Decatur, Ill. The six, all with previous discipline problems, were tossed for going on a rampage at a Sept. 17 high school football game.

Mr. Jackson was arrested leading a protest against the two-year expulsions, which were later reduced to one year.

A judge is set to rule early this month on whether the school acted improperly in expelling the six. Part of the students' case is that zero tolerance weighs more heavily on blacks. In Decatur, more than 80% of all students kicked out of school in the past three years were black even though blacks make up less than half the student body.

The same trend has been seen across the United States. According to a study by the Applied Research Centre of Oakland, Calif., in San Francisco, blacks constituted 16% of students but accounted for 52% of the removals from school on disciplinary grounds.

In Phoenix, blacks made up only 4% of the high school student population but received 21% of the expulsions or suspensions. Whites, who made up 74% of students, received only 18% of the expulsions or suspensions.

Zero-tolerance policies largely grew out of a 1994 federal law, the Safe and Drug-Free School Act, which says schools must expel any student found with a weapon, or lose federal aid.

But schools took the idea and ran with it. Now zero tolerance includes things like dress code violations and stiff sanctions for formerly accepted behaviour like schoolyard pushing and shoving.

Teachers and administrators like zero-tolerance policies because they remove discretion and protect schools from lawsuits charging a student was treated unfairly.

"We've had a number of catastrophic school shootings, and parents and teachers want schools to be very safe," said Gerald Tirozzi, executive director of the National Association of Secondary School Principals.

In his view, zero tolerance is actually fairer to students.

"If it's applied evenly across the board, then it's not an issue of whether you are black or white or rich or poor," he said.

The idea of zero tolerance has percolated to Canada, spurred by the same fears of school shootings that fuel the movement in the United States.

Last year, two 13-year-old Manitoba boys were suspended in the wake of the school shootings in Littleton, Colo., after they apparently drew up a "hit list" that included the names of fellow students and a teacher.

An 18-year-old Mississauga, Ont., student was charged after a message was found on a school washroom wall reading: "If you thought Colorado was bad, wait till you see me."

While Canadian zero tolerance also has examples of overreaction, there is no movement now calling for its elimination, said Stuart Auty, president of the Canadian Safe Schools Network.

"From our perspective, it means there will be a demonstrated consequence to an act of violence," he said. "If kids think they can break the rules, they will break the rules."

The U.S. defenders of zero tolerance insist the policy has cut school crime and made classrooms safer, even if there have been occasional abuses that make juicy headlines.

But the budding anti-zero-tolerance movement says removing teacher discretion and enforcing rigid rules leads to problems that call the whole concept into question.

"You teach kids that the system is crazy," said Mr. Whitehead. "When I was a kid and put a tack on someone's chair, the school would call my mom. Now, parents have become the enemy because they have to sue to get their kids back in school."