The war, now in its seventh month, has killed more than 34,000 Palestinians, according to Gaza health authorities
There were no children among those killed in the shelling at School No. 57 on the first day of the new school year, though witnesses said the dead included a biology teacher and the parent of a child at the school.
Reuters correspondents saw the bodies of three adults at the school and an additional six bodies in a burnt-out mini-van and on streets nearby. The regional administration said a total of 10 people had been killed in the shelling of the city, a stronghold of rebels waging a separatist rebellion.