Most of those killed in the attack were children.
The Taliban say the attack was revenge, after Pakistani authorities killed their members.
At least six fighters entered the military-run school in the Pakistani province of Peshawar, while exams were taking place.
It's thought the Muslim extremists fired indiscriminately.
The Anglican Bishop of Peshawar, Rt Revd Humphrey Peters, told Premier: "There'll be three days mourning in the province... and then we have cancelled all our Christmas celebrations because it is very disturbing - very very disturbing."
"We are totally with the families of our majority community Muslim brother and sisters. We are in solidarity with them."
"I really can't say it, but it's become a conventional thing... Peshawar is so quiet now. Everyone is so sad.
"I will question the intelligence agencies. Where are they? Why can't they pick it up? What are they there for?
"We need a lot of prayers. The church, being the marginalised and the minority and the poorest of the poor, we are worried about the security of our churches and our institutions.
"It is very very expensive to keep two or three guards. Security-wise we people are really weak."