Five students who say they were victims of homophobic bullying are suing a Minnesota school district over an “epidemic of harassment”.

They say that the Anoka-Hennepin School District, the state’s largest, failed to protect them and that a “gag policy” restricting teachers’ ability to discuss gay and lesbian issues made the problem worse.

According to the lawsuit, filed at the US District Court for the District of Minnesota, the students faced daily abuse, threats, violence and humiliation, including “being urinated on, being stabbed in the neck with a pencil, being choked, being pushed into walls, being shoved forcefully into lockers [and] having objects thrown at them in class”.

The complaint adds that many attacks took place in view of school officials but no action was taken. Instead, the bullied students were told to “ignore” the harassment or were even told they were to blame for it, through their behaviour or appearance.

Three of the five students are LGB – one is lesbian, one is gay and one is bisexual. The other two are heterosexual and were bullied because they were perceived to be gay. One has gay parents.

The lesbian student attempted suicide after being forced to leave her school, the lawsuit says. All of the students suffered anxiety or depression and their grades fell as a result of the harassment.

In the nine-month period between November 2009 and July 2010, at least four LGBT students in the district killed themselves.

The students, aged between 14 and 18, are being represented by the National Center for Lesbian Rights (NCLR) and the Southern Poverty Law Center.

NCLR executive director Kate Kendell said: “There is something seriously wrong in the Anoka-Hennepin School District, and district officials know it.

“In school after school, kids who are perceived as gay are harassed mercilessly until they drop out, melt down or lash back.

“This epidemic of harassment – unlike anything we’ve seen in neighbouring districts – is plainly fuelled by the district’s shameful and illegal policy singling out LGBT people and LGBT people alone for total exclusion from acknowledgement within the classroom.”

The lawsuit demands the end of the district’s ‘neutrality policy’ on gay and lesbian issues, as well as damages for the plaintiffs.

Anoka-Hennepin School District’s policy says that “in the course of their professional duties [teachers must] remain neutral on matters regarding sexual orientation.”

While the school district argues that this is a “neutrality policy”, gay rights campaigners call it a “gag clause” which prevents teachers from supporting LGBT students and stops them acting fully to prevent homophobic bullying.

After a spate of suicides, the US Justice and Education departments began investigating the district last November.