A quick-thinking teacher turned hero today when she saved a woman’s life while on her lunch break at a Brooklyn eatery.

Cassandra Byrd-Scolaro, 34, was grabbing a wrap at S&B Restaurant on Bedford Avenue in Williamsburg just before noon when there was a commotion in the bathroom.

A waitress broke down the door, and found a 25-year-old victim who was not breathing.

“We all just sprung into action,” the fourth-grade P.S. 17 teacher told The Post. “I started doing compressions.”

Byrd-Scolaro, who’s worked as a teacher for a decade, performed CPR for about 3 minutes until EMS arrived.

“As a teacher we are trained responders. In real life, this is the first time I’ve used it,”

“I’m happy we were here,” she said.

Byrd-Scolaro clapped when emergency workers brought the conscious victim out of the restaurant on a stretcher.

“It’s good, it’s good.” she said before heading back to school.

The restaurant gave her lunch on the house.

The victim was later taken to Woodhull Hospital in stable condition.