It is believed that his friends ran into the school, but he got hold of the suicide bomber who detonated his vest.
There has been an outpouring of praise and gratitude on social media ever since news of his actions became known.
There have even been calls for him to receive the army’s highest honour awarded to those who have sacrificed their life for their country, though it is unclear if he would be qualified to receive it as a civilian.
“We the citizens believe that State of Pk must award Nishan-i-Haider to Pk’s brave son Shaheed Aitezaz,” journalist Nasim Zehra tweeted on Thursday.
The incident took place on Monday in the Ibrahimzai, a Shia-dominated region of Hangu, in north-western Pakistan. There were almost 2,000 students in attendance at the time of the attack, media reports say.
On Twitter, users are paying tribute to Aitzaz using the hashtags #onemillionaitzaz and #AitzazBraveheart echoing the language used online around figures such as Pakistani education campaigner Malala Yousafzai and the Delhi rape victim, whose death galvanised Indian public opinion and prompted changes in rape laws.
His family have also spoken of Aitzaz’s actions in Pakistan’s Express Tribune newspaper.
“My son made his mother cry, but saved hundreds of mothers from crying for their children,” Mujahid Ali, Aitzaz’s father is quoted as saying.