Indiana teachers undergoing active-shooter training got a more realistic experience than they bargained for, when cops shot them “execution style” with pellet guns, drawing blood, according to their union and a report.

During the January training, cops led unsuspecting teachers into a classroom, had them kneel against a wall, then blasted them from behind with airsoft guns — all to teach them a lesson about the dangers of sitting idly by during a school shooting.

“They told us, ‘This is what happens if you just cower and do nothing,’” one teacher told the Indianapolis Star. “They shot all of us across our backs. I was hit four times.”

The state teachers union said that the point-blank shots during the drill left very real injuries.

“During [an] active shooter drill, four teachers at a time were taken into a room, told to crouch down and were shot execution style with some sort of projectiles – resulting in injuries to the extent that welts appeared and blood was drawn,” tweeted the Indiana State Teachers Association on Wednesday.

“The teachers were terrified, but were told not to tell anyone what happened,” the union added in another tweet — just so the cops could allegedly keep the surprise intact for their next batch of trainees. “Teachers waiting outside that heard the screaming were brought into the room four at a time and the shooting process was repeated.”

Local Sheriff Bill Brooks, whose department carried out the training, insisted the teachers knew what they signed up for.

“They all knew they could be [shot]” with the 4.6-millimeter plastic pellets, Brooks told The Star. “It’s a shooting exercise.”

But the teachers told the paper that while they were given paintball masks as a precaution in case of accidents, they had no warning that they would be shot intentionally.

The teachers union wants a pending bill on active-shooter training in schools to include language banning instructors from using their trainees for target practice, the report said.