Students held fundraisers to make the $130 needed to buy the pole and the flag, and a parent poured the concrete to put it up.
On Thursday morning, a teacher and her students noticed the flagpole was gone.
"When I saw it, I tried to turn around and head them back into the classroom, and one of the kids saw it and said, 'They stole our flagpole, how could they do that to us?'" said assistant teacher Mari Huscher.
The students are already planning another fundraiser to replace the flagpole.
Police suspect the thieves will try to sell the flagpole as scrap metal. They say they've seen a spike in metal thefts as the price of scrap metal goes up.