An armed gang abducted three primary school teachers in the northwest Nigerian state of Kaduna on Monday.

It marks the first raid on an elementary school in a wave of abductions at educational institutions by gangs, usually referred to by authorities as bandits, in which more than 700 people have been taken since December.

Kidnap for ransom has become common in parts of the northwest in recent years. President Muhammadu Buhari in late February urged state governments to “review their policy of rewarding bandits with money and vehicles, warning that the policy might boomerang disastrously.”

Here are details of schools targeted recently:

* Gunmen kidnapped 344 boys from the Government Science Secondary School in the northwestern state of Katsina during a night-time raid on Dec. 11, state officials said.

The boys were rescued by security forces on Dec. 18. They said they had been held in a forest by the criminal gang.

* An armed gang in north-central Niger state killed a student and abducted 42 people, including 27 students, in the early hours of Feb. 17, the state governor said.

The attackers targeted the Government Science Secondary School in the Kagara district of Niger state. All 42 captives were released on Feb. 27, said state officials.

* Attackers stormed the Government Girls Science Secondary School in the town of Jangebe in northwestern Zamfara state in the early hours of Feb. 26, the state governor said.

Governor Bello Matawalle initially said 317 girls were taken in the raid. But he revised that number down to 279 when they were released on March 2. Matawalle said some girls had escaped in the melee following the attack.

* A forestry college in the northwestern state of Kaduna was targeted by attackers who stormed its compound late on March 11, taking dozens of students, according to state security commissioner Samuel Aruwan.

The Federal College of Forestry Mechanization sits on the outskirts of Kaduna, the state’s capital city, near a military academy. The army later said it had rescued around 180 people but the attackers fled with around 30 students. Aruwan later said nine more students than originally thought were missing, taking the total to 39.

A video of some of the kidnapped students emerged two days after the raid, showing them cowering on a forest floor as armed captors hit them with sticks. The footage showed around two dozen students begging for help. One says the captors want a 500 million naira ($1.31 million) ransom.

* Gunmen on motorcycles stormed a primary school in the Birnin Gwari local government area of Kaduna on March 15 and kidnapped three teachers, a Kaduna state government official said. He said no children had been abducted.

The kidnappings came one day after Kaduna state officials said an attack by an armed gang at another school had been repelled by the police and army.

($1 = 380.5500 naira)