From the Latin quies (quiet ).  Today's adjective quiescent traces back to the Latin verb quiēscere, meaning "to become quiet" or "to rest," and was possibly first used by Francis Bacon, who wrote in 1605 that "… as Aristotle endeavoureth to prove, that in all motion there is some point quiescent…" Way to bring it home, Bacon.

When I was in kindergarten, many, many moons ago, there was a required quiescent period called nap time.  And that's back when kindergarten only lasted for a half-day.  

Just the facts:

Quiescent Definition & Meaning - Merriam-Webster

1 hour ago, drpaladin said:

The same practice followed to the first grade. No idea if it's still done.

I didn't have any nap time after kindergarten, and none of my children had nap time while in public school, only when they were in nursery school.