It's not impossible that the Israelis screwed the pooch on the targetting intel, they're no more perfect than any other military organization. Shit happens. So what.
As far as 'Civilized' rules go, the IDF is only in the wrong if they blew it up knowing it was a school, and strictly because it was a school.
While our own approach to rules of engagement is smarter than it was in Viet Nam, it still vastly restricts anything that'll do significant collateral damage to protected sites or civilians, far more so than the real law of war actually requires. Our ROE are driven by the Law of Adverse Press Coverage, not the Law of War, and so the Israelis don't suffer from quite as many self-imposed obstacles as we do. The DUmmies however think the rest of the world is the US, and everyone except our enemies should play by the same crippling rules we use. Idiots.