The strike hit the Jaffa school in the Tufah neighbourhood, causing a fire that spread through tents housing families. Among the dead were five-year-old twin girls.
There was no immediate comment from the Israeli military, but it maintains that the operations target militants and accuses Hamas of operating within civilian areas.
Gaza's health ministry says over 51,000 Palestinians have died since the war began in October, though it does not distinguish between fighters and civilians. Israel claims around 20,000 of those killed were militants, without providing evidence.
