Militants were said to have approached the school in military fatigues and were reported to have detonated several suicide vests before indiscriminately shooting children and adults.
There has been widespread criticism of the attack - British prime minister David Cameron called it "horrifying" and "deeply shocking", teenage activist Malala Yousafzai said she was "heartbroken" and the Pakistani prime minister called the attack a "national tragedy".
In fact, the massacre, which was said to be in retaliation to anti-Taliban military offensives, was even condemned by other Islamist militant groups.
"This was carried out by the enemies of Islam. It is open terrorism,” said Hafiz Saeed, the leader of Lashkar-e-Taiba, the group which is said to have carried out the terrorist attacks on Mumbai in 2008. “These are barbarians operating under the name of jihad,” he told the Wall Street Journal.
Zabihullah Mujahid, a spokesman for the Afghan Taliban, said: "The intentional killing of innocent people, children and women are against the basics of Islam and this criteria has to be considered by every Islamic party and government."