Beijing ? Armed police will patrol schools in China’s capital after a farmer attacked kindergarten students with a hammer, then burned himself to death Friday in the third classroom assault in as many days.

The government ordered schools across the country to tighten security, and anxious parents of students targeted in an earlier attack marched in protest Friday night, demanding a better government response to the crisis.

In the latest assault, Wang Yonglai used a motorcycle to break down the gate of the Shangzhuang Primary School in the city of Weifang and struck a teacher who tried to block him before hitting students with a hammer, the official Xinhua News Agency said.

Wang then grabbed two children, poured gasoline over his body, and set himself on fire. Teachers pulled the children to safety, but Wang died. None of the five injured students had life-threatening wounds, Xinhua said.

The attack was confirmed by an employee at the Weifang Public Security information office. Wang’s motive was unclear. Xinhua described him only as a farmer.

Chinese schools have had five such attacks in just over a month — unusual in a country where extreme violence is comparatively rare and strict controls keep most people from owning guns. Sociologists suspect the rampages — usually by lone, male attackers — could be copycat actions.

State media reports have largely shied away from why students have been targets. Experts say outbursts against defenseless children can be due to social pressures in a rapidly changing society.

The attacks have been particularly shocking because most urban families in China have only one child because of government population control policies.

“Children are the ones people care about the most, and they are the most innocent,” said Ma Ai, a sociology professor at the China University of Political Sciences and Law in Beijing.

Targeting children is “beyond the bottom line of human morals,” he said.

State media either ignored or played down Friday’s attack. It wasn’t mentioned on the evening news in the eastern province of Shandong, where it occurred, and Xinhua didn’t release a Chinese-language story on its website. Experts have worried openly about copycats, but authorities may also have wanted to avoid overshadowing Friday’s opening of the World Expo in Shanghai, a pet government project.