She’s a Grade A donor.

A Long Island woman gave her kidney to her former fifth-grade English teacher she once “could not stand” after the two reconnected decades later and she was moved by his desperate plea for help.

Montana Miller, 55, made the life-saving act to her onetime classroom nemesis, Mitchell Grosky, in April after he posted on Facebook last summer he was in the final stages of kidney disease and praying someone would give him the “gift of life,” The Boston Globe reported.

Frustrated by commenters offering the ailing 74-year-old nothing but thoughts and prayers, Miller got herself tested – and despite having different blood types – she learned in December the pair were a match. 

“I wanted to help Mitch so badly that it became almost painful,” she told the outlet.

Her 10-year-old self – then a Massachusetts middle school student – would have felt very differently.

Miller, a trapeze artist who earned her PhD in folklore and mythology from UCLA, said she used to dread attending Grosky’s reading class at The Bromfield School in 1980, noting the two constantly clashed because she found his assignments too easy. 

“I absolutely could not stand him,” she told the Globe.

 “It was a battle of the minds, a battle of wills.”

The two reconnected on Facebook in 2012 and “became friends,” forming a newly forged bond and a mutual respect for each other and what they had accomplished in the decades since their days abutting heads. 

Grosky hailed his former pupil as the “most brilliant, most creative student” he’s ever had, while Miller said the “pride” he has for who she was and who she has become has been deeply “healing for her.”

The pair shared adjoining operating rooms at UMass Memorial Medical Center, where doctors successfully transferred Miller’s right kidney to the former Athol, Massachusetts principal on April 21. 

“The pain I’m going through now is definitely not more than I can handle,” Miller told the outlet, writing on Facebook that she and Grosky are both “painfully but positively on the road to recovery.”

“It almost feels good, like this pain is something that is a privilege.”

Grosky, who is recovering at his Athol home with his wife, remains “astounded and almost perplexed” that Miller stepped up to help save his life, and hopes to pay that kindness forward.

“Awesome has become a slang term,” he told the outlet. 

“But awesome when you look at the Grand Canyon. Awesome is when you see pictures of the moon. She comes closest to anybody I’ve ever known to really being awesome, in the truest sense of the world.”