Those assemblies can tend toward stultifying. But not so in West Des Moines, Iowa, where a bunch of teachers joined forces last week to interrupt their superintendent — and surprise and delight their colleagues.

With one more day of planning left before classes began, the teachers sang a parody version of “One More Day, the soaring anthem from the Broadway musical “Les Miserables.”

The performance was recorded and posted to YouTube, along with the full set of new lyrics for the song (skip ahead to the 1:20 mark to watch).

“One more day all on my own,” they sing.  “Do we know the Common Core? No more time for preparation. Will my lesson be a bore?”

You can’t watch this video without thinking that these teachers must have some pretty lucky students. Their voices are impressive. And their colleagues are clearly appreciative.

“One more day to education, we will help these students grow! We’ll be ready for these schoolboys. We will teach what they don’t know!”

West Des Moines students started class on Monday, according to the Des Moines Register, which first reported the flash mob.

“It was just to bring some fun and energy to the welcome back,”school system spokeswoman Elaine Watkins-Miller told the Register.