Garland, Texas — If you needed proof that 85-year-old Sharon Bradley is pretty much unstoppable, there's the cast on her hand. She broke it in a fall Sunday and went to work the very next day.

"I wouldn't miss class for a broken bone," she said.

Bradley teaches health science at Naaman Forest High School outside Dallas and has not missed one single day in 26 years. She didn't miss class when her house was damaged by a tornado, or when her dear husband, Jack, passed away.

"I had done all I could for him okay? And so, I really felt like I had a responsibility to these kids," Bradley said.

Sharon Bradley CBS News

That sense of duty goes back to her days as a nurse. She was at Parkland Hospital the day President Kennedy was shot and brought into the emergency room. But her legacy is in the classroom.

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So on her 85th birthday, the school surprised her with a party to celebrate her perfect attendance and attitude.

"I think the more positive you are the healthier you are, OK, the more fun you have in life," Bradley said.

From September to June she's having the time of her life. But come summer, "Oh, I mope," she said. She scoffs at the idea of retirement.

"Boring," she said. "I'd rather be in the classroom, this is fun."