As reported by Tariq Arian, spokesman for the ministry, the number of wounded in the attack on Saturday also rose to more than 100.
Three explosive devices were detonated at the entrance of the school when the students were leaving after their school day, the spokesman said.
The school is located in a neighborhood with a majority of Shiite Muslims, in the western sector of Kabul, and where that community suffered several attacks, often claimed by the Afghan branch of the terrorist group Islamic State.
The Talibans denied being responsible for the attack on the educational center and condemned it.
So far no one has claimed responsibility for the attack, the first reports of which referred to 27 people killed and 46 injured, as per the 1TV television network.