About a year ago, the novelist Neil Gaiman delivered a lecture at the Barbican, in London, on behalf of the Reading Agency, a not-for-profit organization that promotes literacy and reading for pleasure among children and adults. In the lecture, which was reprinted in the Guardian, Gaiman came out in favor of what might be called the “just so long as they’re reading” camp.

“I don’t think there is such a thing as a bad book for children,” he argued, adding that it was “snobbery and … foolishness” to suggest that a certain author or particular genre might be a baleful influence upon young reading minds—be it comic books or the works of R. L. Stine. Fiction is a “gateway drug” to reading, Gaiman said. “Every child is different. They can find the stories they need to, and they bring themselves to stories. A hackneyed, worn-out idea isn’t hackneyed and worn out to them.” Well-meaning adults, he continued, can easily kill a child’s love of reading: “Stop them reading what they enjoy, or give them worthy-but-dull books that you like, the 21st-century equivalents of Victorian ‘improving’ literature. You’ll wind up with a generation convinced that reading is uncool and worse, unpleasant.”

The opposite argument—that the kind of book a child has his or her nose buried in does make a difference—has been mounted elsewhere, notably by Tim Parks, in an essay that appeared on the blog of the New York Review of Books. “If the ‘I-don’t-mind-people-reading-Twilight-because-it-could-lead-to-higher-things’ platitude continues to be trotted out, it is because despite all the blurring that has occurred over recent years, we still have no trouble recognizing the difference between the repetitive formula offering easy pleasure and the more strenuous attempt to engage with the world in new ways,” Parks wrote. He enlisted the example of his own children’s reading habits, and those of his young students, to argue that there is little evidence to suggest that readers will make progress “upward from pulp to Proust.” “I seriously doubt if E.L. James is the first step toward Shakespeare,” he concluded. “Better to start with Romeo and Juliet.”

This debate came to mind earlier this month at the New York Public Library, when Rick Riordan, the author of the best-selling Percy Jackson series, was in town to promote “The Blood of Olympus,” the latest and final volume in his second cycle of novels drawing upon Greek mythology. The first, “Percy Jackson and the Olympians,” has sold upwards of twenty million copies worldwide, and more than three hundred of his young fans filled the Celeste Bartos Forum at the library, where Hyperion, Riordan’s publisher, had placed promotional T-shirts and temporary tattoos on every seat, and had ranged stacks of signed volumes for purchase. The atmosphere was one of high excitement and engagement, and if it is true that I have seen adult audiences in that venue similarly riveted by the presence of an author—Karl Ove Knausgaard’s rock-star appearance earlier this year, for example—I have yet to attend a literary event at which the presence of the author, or the mere mention of his most popular characters, has been met by uncontrollable squealing.

For those unfamiliar with the Riordan’s Olympian fictions—which is to say, people without children between the ages of seven and seventeen—their hero, Percy Jackson, thinks he is just a kid with a learning disability and a troublesome tendency to get kicked out of school, until he learns that his difficulties can be explained by the fact that he is a demigod, the offspring of Poseidon and a mortal woman. In the first book of the series, “The Lightning Thief,” Percy gets shipped off, at the age of twelve, to Camp Half Blood, a refuge on Long Island populated by his demigod peers. There he learns the skills becoming of his lineage—sword fighting looms large—and discovers his own peculiar gifts: even when injured, he is miraculously healed and empowered by water.

Riordan has come up with a clever conceit, which is amusingly sustained. Medusa is the proprietress of a garden center in New Jersey that sells lifelike statuary: no prizes for guessing how the stock is replenished. Ares, the god of war, is a biker in a red muscle shirt who comes armed with a huge knife. (“I love this country. Best place since Sparta,” he says.) A detour to Las Vegas finds Percy and his pals beguiled by the attractions of a casino: video games, laser tag, indoor skiing. The seductive spell of indolence is broken after Percy falls into a disconcerting conversation with a kid in bell-bottoms, who refers to something or other as “groovy.” The bell-bottomed kid has been trapped in the—of course—Lotus Casino since 1977, though he thinks it’s only been a couple of weeks. Percy, as narrator, says, “I said something was ‘sick,’ and he looked at me kind of startled, as if he’d never heard the word used that way before.”

That slangy, casual style is a hallmark of the Percy Jackson books, which often read like a faithful transcription of teen uptalk. At the level of language, Riordan’s books make J. K. Rowling’s “Harry Potter” series seem as if it were written by Samuel Johnson. Unlike the Harry Potter books, which, notoriously, have been embraced by adult readers as well as juvenile ones, the Percy Jackson books seem positively contrived to repel adult readers, so thoroughgoing is their affectation of teen goofiness.

Riordan is a former middle-school English and history teacher, and at the N.Y.P.L. he revealed himself to have the ingratiating informality strategically adopted by some of the best and most beloved teachers. In a PowerPoint presentation, he showed photos of himself as a nerdy kid, said that the first book he read for pleasure was “The Lord of the Rings,” talked about his love of comics, and showed the first rejection letter he’d received, for a story he’d submitted to a magazine as a teen-ager. Riordan’s tale of his publishing career was, perhaps, oddly pitched for a pre-teen and teen-aged audience; when he revealed that the advance he received for his first novel was fifteen thousand dollars, my nine-year-old son whispered to me, “That’s a lot of money.” Then again, Riordan’s sense of what kids will find interesting or funny is clearly highly attuned, even if it might occasionally strike other, less best-selling adults as somewhat peculiar. The other day, my son read aloud to me an extended joke involving H.M.O.s and deductibles from “The Blood of Olympus,” which he found hilarious in spite of his ignorance of the mysteries underpinning America’s health-insurance infrastructure.

Riordan’s books prompt an uneasy interrogation of the premise underlying the “so long as they’re reading” side of the debate—at least among those of us who want to share Neil Gaiman’s optimistic view that all reading is good reading, and yet find ourselves by disposition closer to the Tim Parks end of the spectrum, worried that those books on our children’s shelves that offer easy gratification are crowding out the different pleasures that may be offered by less grabby volumes. Undoubtedly, Riordan has single-handedly sparked an enthusiasm among young readers for Greek mythology, and if kids are dressing up for Halloween as Apollo or Poseidon instead of Iron Man or a generic zombie, so much the better. My son and his peers know the tales of the Greek gods far better than I do, and if some of that is due to reading books such as Mary Pope Osborne’s wonderfully ungimmicky “Tales from the Odyssey,” or from having “D’Aulaires’ Book of Greek Myths” in the read-aloud rotation from an early age, a good measure of that familiarity has also come via Riordan’s retellings.