The school was housing displaced residents. Dozens were injured in the attack.
Israeli military aircraft targeted the school while worshippers were performing the fajr (dawn) prayer, the Palestinian news agency, Wafa, reported.
The Government Media Office in Gaza condemned the school “massacre,” saying that the attack is “part of a broader campaign of genocide and ethnic cleansing against the Palestinian people.”
In a statement, the media office said: “The occupation army directly targeted displaced civilians while performing fajr (dawn) prayers, (which) led to a rapid rise in the number of casualties.”
It placed “full responsibility for the massacre on the Israeli occupation and the US administration.”
The media office also urged the international community and global organizations to “put pressure on Israel to stop the ongoing genocide and ethnic cleansing of civilians and displaced people in the Gaza Strip.”
Meanwhile, the Israeli army claimed the school contained an “operating military headquarters” for the Palestinian group Hamas.
It claimed that “several steps were taken to minimize the risk of civilian harm.”
With the bombing of Al-Taba'een School, the total number of schools targeted by the Israeli army in Gaza City over the past week has increased to six, according to an Anadolu tally.
Despite appeals on Thursday from mediators, including Egypt, the US, and Qatar, to stop hostilities, reach a cease-fire, and a hostage exchange agreement, Israel persists with its deadly offensive on the Gaza Strip.
This escalation came amid threats of retaliation by Lebanon’s Hezbollah group following the assassination of its top commander, Fuad Shukr, in an Israeli airstrike on Beirut on July 30 and Iran's threats to retaliate after the assassination of Hamas political bureau chief Ismail Haniyeh in the capital Tehran on July 31, an attack attributed to Tel Aviv.
The Israeli onslaught against the Gaza Strip has killed nearly 39,700 people since last October following a cross-border attack by the Palestinian resistance group Hamas.
More than 10 months into the Israeli onslaught, vast tracts of Gaza lie in ruins amid a crippling blockade of food, clean water and medicine.
Israel is accused of genocide at the International Court of Justice (ICJ), which ordered it to immediately halt its military operation in the southern city of Rafah, where more than 1 million Palestinians had sought refuge from the war before it was invaded on May 6.