Most weekday mornings Lauren Tarshis tries to catch the 7:51 Metro North train from Westport to get to her desk at Scholastic, the children’s book and magazine publisher, which has secondary fame as the house of Harry Potter.

Since July, Tarshis has been editor-in-chief of Scholastic’s classroom magazine division. A 30-year veteran who started as writer of news articles for teens, she now oversees a dozen titles with a combined readership of around 15 million. Hers is a big job, but it’s still a day job.

Most of those same weekday mornings, the author Lauren Tarshis arises at 4:30 to work on the latest installment in her “I Survived” series of historical fictions. It’s a niche series, written for middle schoolers, with special appeal to older ones who may be reluctant readers, that nevertheless is astonishingly popular.

With the publication in January of the 18th volume, “I Survived, the Battle of D-Day, 1944,” Tarshis estimates total sales have surpassed 30 million since the series launch in 2010 with “I Survived, the Sinking of the Titanic, 1912.”

Each volume runs roughly 100 pages with illustrations and is deeply researched by Tarshis herself. For the book about D-Day she went to Normandy. She doesn’t alter historical facts, but does fashion a dramatic personal story for her protagonist, usually a boy. Usually, too, she introduces him in a short first chapter that ends with a cliffhanging bang.

In the Titanic story, the reader discovers 10-year-old George Calder on the deck of the sinking ocean liner, “more scared than he’d ever been.” He falls, bangs his head. “Then George couldn’t see anything. Even the stars seemed to go black.”

In D-Day, 11-year-old Paul Colbert is on a cliff overlooking Omaha Beach when a burning plane falls toward him. “The engine screamed and moaned. It sounded like a giant beast bellowing in pain.” He runs but is hit by a piece of wreckage. “Paul had been praying for this day ... for France to be finally free from the Nazis. But now it seemed this day would be his last.”

As easy and exciting as the books may be to read, the writing of them has an almost inverse degree of difficulty exactly because Tarshis must compress epic events — their meaning and feeling — into 10,000 or so age-appropriate words.

“I do so many drafts, it’s a nightmare for my editors. I may spend a week writing two paragraphs to crystalize a story,” she says, thinking of an 800-word passage on immigration she wrote for her newest project, the Great Boston Molasses flood of 1919.

Each book is layered, she says, with the focus shifting back and forth between the event itself, the protagonist’s immediate experience and his or her backstory.

In volume six, “I Survived, the Attacks of September 11, 2001,” the main character finds himself in a fire station near the World Trade Center because he has gone there to plead his case to his firefighter father’s best friend that he be allowed to play football despite having sustained concussions.

Tarshis says demand from her fan base overcame her reluctance to take on the 9/11 attacks. She herself learned of the attacks when her flight back home from London made a u-turn. In New York, colleagues could see the burning towers from the roof of the Scholastic building.

Though she wrote the book on 10th anniversary of the attacks, Tarshis doesn’t see her decision to make football concussions part of the story as prescient. As the then editor of Scholastic’s “Storyworks” magazine, she was aware of the injury issue. Closer to to home, she recalls Westport parents worried about players “getting dinged.”

Tarshis qualifies as a Westporter twice over. She and her husband moved back there to raise four now mostly grown children. But Tarshis herself first came to Westport as an 11-year-old living with a secret. She spent most of her childhood hiding her own extreme reading reluctance.

“My story as an author is it’s truly impossible I would be sitting at this desk,” she says. “I did not read as a kid. I had real struggles. I had fears related to being found out and related to being not smart and to being quite certain I would never be able to do anything.

“I had all sorts of tricks, like listening in on friends. I made it through Coleytown Junior High, but 10th grade was the first year of high school and I thought, ‘What are they going to do with me? Will I be sent back to elementary school?’ ”

Tarshis says she otherwise had a happy childhood. Her father worked as a freelance magazine writer and her mother taught special education in Fairfield and Redding. She now sees her problem was one of synthesis and thinks her cover up worked partly because there was less emphasis on being “a reader.”

The first complete book Tarshis ever read was “Tale of Two Cities,” assigned by a Staples High teacher whose name she still remembers. Challenging herself, she learned that by reading every paragraph a couple of times, very slowly the book would open itself to her.

Her skills so improved that she eventually graduated from Barnard College, where she wrote for the shared Columbia Daily Spectator student newspaper. Still she had gaps. When she got promoted to editor of “Storyworks,” she went to the Westport Library to give herself a crash course in the children’s classics she had skipped. She now thinks her reading woes inform her work both as editor and author.

“I don’t assume kids will understand anything,” she says. “Even kids who are not readers are curious and want to be engaged and know stuff, if you can give them content with a story.”

From the start, she expected the “I Survived” books to be used in classrooms. Each comes with a teacher’s guide and often a documentary appendix. Individual books in the series have won many awards.

Tarshis got the idea while planning the third in a series of longer novels she wrote for middle school girls. The first, “Emma-Jean Lazarus Fell Out of a Tree,” was published in 2007 by Dial and was named to several best book lists.

She says she became “emboldened” to attempt a novel during her reading binge for “Storyworks.” Her first failed attempts convinced her she had no talent. But she kept on, encouraged by her journalist father and an encounter with J.K. Rowling, who had come to Scholastic to help with publicity.

“I was dazzled by her,” Tarshis says, and heartened by Rowling’s earned wisdom, “Don’t you think a person has to write one terrible book?”

Joel Lang is a frequent contributor to Sunday Arts & Style.