That exactly is the verb ("to retard"). You might mean the noun "a retard" which does not have good uses I can think of.
Retardant, retardation, retarding, retarded and a ton of other drives words also do indeed have actual real world meanings and uses that have nothing to do with humans.
I didn't even know Skype has messenger features. I've only come across it as a really crappy (but good at dealing with firewalls) video conference thing. And evil, of course.
Your first stop might be the website of whatever service/city/school might be responsible. Actually even the ones that aren't might have some info or links. I'd expect they at least provide links on the right direction.
The bureaucracy and correctness of instructions involved may vary a lot, but at least you should find some more specific questions and places to ask/confirm.
I don't think it's quite consistent across the country and system. But I'm old and out of the loop and would be happy to be wrong.
Has been for a few decades at least, but now the targeting is more random.