The jewel of Gaza's bare-bones education system — a U.S.-style school on lush grounds overlooking the Mediterranean — is now a mound of broken concrete. The territory's only laboratory for genetic testing, at a Gaza university, lies in ruins.

With 37 primary and secondary schools destroyed or damaged by air strikes, and 18 others still serving as refugee shelters, learning in Gaza has become even more of a struggle.

Israel says the attacks on schools struck militants and a weapons lab during its three-week war against Hamas. Gaza educators say Israel hasn't provided proof to back up its claims, adding the strikes on some of its best educational institutions set back efforts to develop the impoverished territory.

Even before the offensive, overcrowding had forced most of Gaza's 380 primary and secondary schools to run morning and afternoon shifts of no more than four hours each to accommodate 450,000 students.

The American International School of Gaza, near the northern town of Beit Lahiya, stood apart from the rest. Sitting on an 8-acre plot, it was an oasis in dusty and crowded Gaza, with its lawns, palm trees and roses.

Founded by Gaza academics in 1999, the school taught in English, followed a U.S. curriculum and offered field hockey and American football along with academics, to children from kindergarten through 12th grade.

"This was a great school," said Shareefa el-Helou, 17, who now crams for SATs in math and biology at an uncle's home because her family's apartment was damaged in the fighting. "We used to do fun days, sports days, bake sales."

Since 2004, suspected Islamic extremists repeatedly targeted the school, presumably over its Western outlook and coed system. Assailants burned five of the six school buses and mortar attacks destroyed the administration offices, art room and cafeteria.

Still, the school kept going. This year it had 220 students, who were on Christmas break when the offensive began Dec. 27.

A week later, an Israeli warplane flattened the two-story school building.

During a recent visit, glass shards were scattered across the ground. Tank treads were still visible, leading from a crushed gate to a flattened slide in the kindergarten playground.

Shredded books stuck out from rubble. A copy of the 2006-07 yearbook lay amid broken concrete, dusty but intact. "Our leaders of tomorrow," read the caption under the school photo, showing students sitting on bleachers, dressed in white shirts and navy pants.

Senior Maise Hakoura, 17, said her paperwork is buried under the rubble and that she is worried about getting her high school transcripts to three Canadian colleges on time.

Israel's military says Gaza militants used the campus to launch rockets, turning it into a legitimate target. The military said Monday it was looking into a request for evidence, such as video from unmanned spy planes showing militants in the area.

Israel says it has the right to defend itself, even at the cost of disrupting lives.

Several empty schools and kindergartens in southern Israel were struck by rockets fired from Gaza during the fighting, said Yuval Steinitz, a legislator from the hawkish Likud Party.

"If Hamas is shooting or hiding rockets to shoot from such places (schools) ... would you like us to sit down and see our children getting killed, and not to react?" Steinitz asked.

Other Israelis, however, question the scope of the destruction.

Dovish former Education Minister Yossi Sarid said Gaza's schools should have been off limits unless they were proven militant strongholds. "Since I'm not convinced that this was the case, as far as I'm concerned schools and other educational institutions are not targets for soldiers to shoot at," he said.

Mohammed Nairab, the principal of the international school, said he couldn't prove militants didn't use the compound during the break. But he said the destruction was counterproductive.

"I do see it (the school) as a bridge between the Arab culture and the American culture, and it serves American culture in this respect," said Nairab, a graduate of the University of Texas at Austin.

Gaza's other private schools have a Christian or Islamic affiliation.

The American school will resume classes next week in a three-story building with a small garden in Gaza City. Nairab said the school will eventually rebuild.

In another strike, Israeli warplanes hit the science and engineering labs of the Islamic University in Gaza City, the territory's oldest and biggest college-level institution, with more than 20,000 students.

The university has long been considered a Hamas stronghold. Many of the group's leaders have taught there, from Gaza Prime Minister Ismail Haniyeh to strongman Mahmoud Zahar. At the height of internal Palestinian fighting February 2007, Fatah forces loyal to Hamas' rival, Palestinian President Mahmoud Abbas, attacked the university.

During a recent tour, a poster showing 24 Hamas fighters killed in the war was seen pinned to an outdoor bulletin board.

Israel targeted the school because of military activities there, Israeli government spokesman Mark Regev said. "Hamas was using it as a command and control center, and the labs were used to construct weapons," he said.

University President Kamalain Shaath challenged Israel to prove that weapons were produced in the labs, which he said provided unique services to the community, such as genetics and environmental testing. He claimed Israel was trying to hold Gaza back by targeting some of its most advanced institutions.

Many students at Islamic University are not Hamas followers, but go there because it offers courses not available elsewhere in Gaza, Shaath said.

Mkhaimar Abusad, who teaches political science at the school's main rival, the Fatah-linked Al Azhar University, said the destruction of the labs amounts to collective punishment. "Basically, by destroying one building, it (Israel) is not punishing Hamas, but an entire community," he said.

Associated Press writer Ibrahim Barzak in Gaza City contributed to this report.