Wikipedia says 600, but I have not independently verified that.

Edit: I have indepdendently verified. From the school to the nearest perimeter of the thing that looks like an airfield, 200+ meters. To any structure likely to be targeted, more. I would say there was something military "in town", and the school was not in the middle of military stuff. It was in a civilian area of the town.

Photo obtained with Wikimapia. Several hundred meters off the possible mark (air field).

Possible clue from Time magazine:

According to Amelirad, based on reports from locals in Minab, the school had previously been used as a military facility but was later converted into a school attended by children from a mixture of military and civilian families attracted by lower tuition.

Source:

Shiva Amelirad, a Canada-based representative of the Coordinating Council of Iranian Teachers’ Trade Associations, a network of teachers’ unions in Iran

Speculation: the US targeted the school deliberately, because their software marked it as a military object. The software was not receiving timely intelligence updates. The building had been converted into a school years ago.

And I don't think we have missiles in our arsenal that are bad enough that they would miss a target by 60m. Maybe I'm wrong about that though.

They're referring to how Americans love to shoot up schools. We have constant school shootings, it's only natural we'd take that next step to school bombings.

So far Obama has been pretty good at bombing schools. But that Trump guy might be the goat

In an ideal world, if a strike planner knowingly clicks on a school, they go to prison. If they aren’t given the information to tell apart a school, their boss goes to prison. Unfortunately in the current-time US, as things are - nobody will be held accountable. :(

In an ideal world they would both be in prison regardless of who the bombs killed. Illegal war of aggression is a crime against humanity.

The other option is that this was done by Israel, and we know from Gaza that they actually target children for the Terror effect and because they see Muslims as "vermin" so don't really care that they're children.

I could totally see the Israeli military doing this on purpose "to break the spirit of Iranians" - I mean, the rest of the World has not punished Israel for doing exactly this in Gaza multiple times, so from that side they would get no downsides from committing more of such attrocities, whilst on the side of Israeli Public Opinion, given how widespread and normalized Racism is there (especially Islamophobia, with Muslims commonly described as "violent" and even "vermin"), they will probably get an uptick in public support from this.

My personal theories on this are that it was either some American military person choosing a target based on satellite imagery and mistakenly picking the set of "buildings with a large patio" which is the school rather than the IRGC base or the Israelis purposefully doing it because they can and for them all Iranians are "vermin" hence the young ones too are just more "vermin", not children.

I don't think the American Military is quite to the point of chosing to murder a school filled with children (though they have quite the track record from way back when they were droning Afghanistan of not caring all that much about large numbers of civilian casualties), but the Israeli Military have a lot of recent practice with purposefully targetting children of "vermin" races and are pretty much veterans at it.