Mobile phone footage from Gaza shows the moment on 17 January when a UN school in Beit Lahiya was hit by shellfire on the last day of Israel's three-week offensive.
The burning lumps are consistent with the incendiary device white phosphorus (WP) - which is banned from use within areas of civilian concentration under international weapons agreements.
The UN says at least two artillery rounds emitting phosphorus landed inside the school where 1,600 Palestinians were seeking refuge from the bombardment. A high explosive shell also hit one of the school buildings, killing two boys, aged five and seven.
The Israeli army says the weapons it used in Gaza were all legal, but has launched an investigation into allegations of illegal use of WP.