Renewed fighting between Israel and Gaza in July and August left more than 2,100 Palestinians dead, about three-quarters of them civilians. It also left much of Gaza in ruins.
Israel's death toll is just above 70, and most of those killed were soldiers.
Human Rights Watch said Thursday that some of the Israeli attacks violated international laws.
"Our report issued today found out that in three different cases, Israeli attacks on UNRWA schools in the Gaza strip, where thousands of people were seeking shelter from fighting, were unlawful. In one case, in Beit Hanoun, several mortar shells landed right inside the school. In the Jabalya school: some people had moved from Beit Hanoun to seek shelter after the Beit Hanoun school was hit, moved to Jabalya and then it was hit several days later. Then in Rafah, the third case, we looked at where an advanced missile hit a motorcycle that was right outside the gates of the UNRWA school, killing about 10 people there," said Bill Van Esveld of Human Rights Watch.
Israel has announced its own investigation into the Gaza war operations, including attacks that killed four Palestinian children on a beach and 17 people at a U.N. school. The Human Rights Watch representative said similar Israeli investigations in the past did not produce significant results.
"That's obviously better than doing nothing, but we are concerned and we think the pressure needs to stay on because the Israeli military's record for accountability is extraordinarily poor," said Van Esveld.
The Israel Defense Force has said it had evidence that the school area was used by militants to fire rockets at Israel. Human Rights Watch has condemned the practice of storing weapons in civilian facilities, but said there was no evidence of any military activity in or near the three schools.
A U.N. representative visited Gaza Thursday to assess the needs of civilians who were left destitute by Israeli shelling.
"We need resources. We need funding to rebuild for both the refugees and the non-refugee families in Gaza,” said Robert Turner, UNRWA Director of Operations in Gaza.
The United Nations is urging the lifting of Israel's blockade around Gaza to ease access for humanitarian aid and construction material. During his visit this week, Norwegian Foreign Minister Borge Brende said aid alone is not enough to rebuild Gaza.
"I think this is a question of what to import, but also the possibility of the people in Gaza to build a real life for themselves so they can start to produce, have their small and medium size businesses that usually flourished in this area to again be rebuilt and start to then have a decent income. This is crucial, and we will continue to address it with Israel," said Brende.
Lifting the blockade has been one of the main conditions of Gaza's Hamas leaders during negotiations for the current cease-fire.