Dan Mindich, a beloved English teacher at Punahou School who wrote a book on how to improve schools by giving teachers time to learn from one another, died Monday. He was 48.

Mindich died after he was pulled from the water during the Waikiki Roughwater Swim, a 2.4-mile ocean race.

The cause of death has been deferred pending further studies, the Honolulu Medical Examiner’s Office said.

"He was a beautiful man," his older brother, David Mindich, said by phone from his home in Vermont. "He touched more than a generation of students. He was just extraordinary. People loved him and they felt his love as well."

Mindich and his twin brother, Jeremy, were born in New York City in 1965.

After receiving his master’s degree in education from Stanford University in 1991, he taught for 17 years in middle and high schools in Kenya, Vermont, California and Hawaii. In 2008, he left Hawaii with his family to pursue a doctoral degree in education at Stanford University.

He wrote his dissertation on "professional learning communities" that was later published as a monograph called "Building a Learning Community: A Tale of Two Schools."

Stanford professor Linda Darling-Hammond, Mindich’s adviser, said Mindich researched schools in New Jersey where leadership and teachers were bringing learning communities into existence.

"It was very much like Dan because it was a study on how teachers can collaborate effectively to improve their teaching and improve the schools they work in, which is something he just cared deeply about," she said. "He was a wonderful, very committed teacher."

She said Mindich’s report also showed that teachers in the U.S. have less time to spend with their colleagues to share practices and learn than any other country that also participated in international studies.

"He did a wonderful, very important study about that, which has been published and widely accessed by teachers and school leaders who are interested in doing that work," she said.

His study seemed to reflect what he was already practicing in the classroom.

Former Punahou School social studies teacher John Cheever taught an American studies course with Mindich during Mindich’s first stint at Punahou from 2003 to 2008.

"I never had to worry about him not liking an idea," Cheever said. "It was by far the most satisfying professional collaborative relationship I’ve ever had."

He said the two constantly shared about ideas about tweaking lesson plans to adjust for students in the class. Mindich also used his sense of humor to reach students.

"Not just funny, hilarious," Cheever said. "He found humor in just about everything, human nature, politics."

"He’s going to be missed," he said. "I’m crushed."

After receiving his doctorate from Stanford, Mindich returned to Punahou to teach high school English in 2011. In 2013, he became director of the high school’s summer school.

The school said it is offering on-campus support services for students and faculty.

Kaia Hedlund, Waikiki Roughwater Swim race director, said water safety personnel went to Mindich’s aid after he yelled out and then went underwater just over an hour into the race.

David Mindich said his brother was an athletic person who competed in triathlons and had been an ocean lifeguard in his teens and 20s in Long Island, N.Y. Mindich completed the Waikiki Roughwater Swim in 2013.

"He was in shape his whole adult life and was an avid swimmer," David Mindich said. "It’s a terrible shock. The family feels they lost a great man, great father, great teacher, great brother."

Mindich is survived by a wife and three children.