one asshole doesn't make it institutional.
He was suspended for 10 days. Even more telling is the fact that
he obviously thought it was okay to say that, that he wouldn't be in any trouble for saying such a thing.
Generally speaking, people of an organization - any organization - will act as they are trained, and will normally follow the example set for them by their leaders. If the leader maintains and enforces ethical standards, such will be reflected in his or her subordinates. Conversely, if the leader acts as if not bound by ethics, such will also be reflected by his or her subordinates.
Look at the Obama administration - how many ethics or conflict-of-interest scandals happened? Very few...and those that were reported were often blown way the heck out of proportion.
Now look at the Trump administration - how many ethics or conflict-of-interest scandals have been reported pretty much every single month since he's been in office?
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I'm not trying to be partisan about this, for this is a lesson I learned a long time ago when I was still a strong conservative. Under one captain, there was nothing that our ship could do right. We screwed up in just about every way - we couldn't pass inspections, we couldn't pass sea trials, and our crew morale was low - nobody gave a damn. Then we had
this captain come on board...and all of a sudden we couldn't do anything wrong - in very little time our entire crew was more professional...we suddenly gave a damn. I was a young sailor at the time, and it took me a lot of years to figure out exactly what had happened...
...and what had happened was Captain Davis. He came in and began holding his senior officers to much higher standards than they'd faced before - that, and he personally demonstrated that he gave a damn about the crew. That was when I finally figured out not just how much influence the leader has...but how important is the example he or she sets for subordinates.
That's why the teacher in the OP did what he did - he thought it was okay to do so. And the reason he thought it was okay to do so was almost certainly because that's the kind of attitude he sees among his colleagues in the Teachers Lounge...and if that's the case, then it's because the one in charge hasn't been holding them to high ethical and professional standards. YES, it's possible that this was a one-off, that this was just one guy having one brain fart...
...but the fact that he was only suspended for ten days before he goes back to teaching the same kids should be your first indication that it's not a one-off. It's institutional.