The president of the NUT has criticised Israel's attack on Gaza as "massively disproportionate" and called for a ceasefire to protect the lives of children and end the damage being done to their education.
Bill Greenshields said that attacks by Israel and Hamas were unacceptable and should stop at once.
In a letter to The TES, Mr Greenshields was particularly critical of the action taken by Israel, which has launched an aerial bombardment and a ground invasion of the Gaza strip.
"Schools are at the centre of the accelerating attack, many housing victims of the violence and destruction brought about by bombing, shelling and ground invasion," said Mr Greenshields.
"Many children have died, their final step on a road built over decades by Israeli occupation, border crossing blockade, air strikes, and the denial of life's absolute necessities. The resulting deprivation has massively damaged children's education, and disease and malnutrition plague their lives."
Mr Greenshields's call for peace follows an Israeli bombing of two schools run by the United Nations. More than 40 people are reported to have been killed.
The victims, including children, were taking refuge. The highest death toll occurred when the al-Fakhura school in the Jabaliya refugee camp was hit on Tuesday.
Israeli officials said the school had been targeted because missiles were being fired from them - a claim that was denied by the UN.
The death toll in Gaza has now reached more than 600. As The TES went to press, Israel, which is coming under mounting international pressure, agreed to halt its hostilities for three hours a day.
A spokesman for the Board of Deputies of British Jews said: "All loss of civilian life in Israel and Gaza is a tragedy; of that there is no doubt. When the victims include children, the losses are yet more painful.
"Hamas continues to use heavily populated civilian areas, including schools, to launch their offensive against Israel, and so there can be no doubt about who is responsible when innocent people are caught in the crossfire."
A teacher working at an English-language school on the south coast, who did not want to be named, told The TES that the aunt and cousins of one of her students had been killed in a bomb blast in Gaza last week.
"It is very sad," she said. "There is very little you can do apart from lending a sympathetic ear."
The NUT has a record of speaking out against Israeli attacks on Gaza. Following its annual conference in 2007, it criticised "the continuing and undemocratic harassment of Hamas MPs and representatives, despite the party's overwhelming mandate following the recent elections in Palestine".
The teaching union criticised Israeli bombing of Lebanon in 2006, the war in Afghanistan and acts of terrorism.