If he's still working then they have either finalized the investigation and he's innocent or they determined they couldn't find any reason to charge him. They tend to be overly cautious in a lot of cases so that someone can't come back and say they didn't investigate the claims. They could be doing all sorts of things. You just don't know.
Even if they file charges the school can't let him go or suspend him on supposition. The charges could be false then they'd be opening themselves up to his getting millions from a lawsuit for wrongful termination.
They can't even let him go during a trial, he could be found innocent. The school does not want a riot on their hands and if it comes to choosing they'll choose him because if they don't he has a wonderful grounds for suing the heck out of them and anyone that spread rumors about him.
Had he done the hitting on the school grounds and people had seen him doing it then they might have a different avenue they could follow. f they had huge whelps on their legs in the shape of a hanger then there would be more proof, he may not have had any of those things happen here, he may have been blindsided by these accusations. He is innocent until convicted in a court of law. That's all there is to it.
What if someone started a rumor about you that said you hit your kids with a hanger and the state showed up and removed them. They'd be wrong about it right? What if your co-workers started gossiping about it and the parents went nuts, to the point where you couldn't even work there any more, you lost your kids, your job, your respect, your status as a teacher in good standing, etc....you'd feel differently if it had happened to you. You'd want the school to support you in every way and to keep you working until the outcome was known. If you were found innocent you'd want to stand up and shout it out that it was a lie and that you were not guilty. But your reputation would still be lost and your career would be over no matter if you were innocent or guilty of much worse.