Nina Laden’s board book, Peek-a-Who? (Chronicle, 2000), keeps young readers guessing, but the title’s phenomenal popularity on Amazon has some adults pleasantly surprised, too. Last December the book was the retailing site’s highest ranked children’s picture/board book, as well as the 57th bestselling title overall, selling more than 4000 copies per week.

Though the book has consistently racked up steady sales of between 20,000 and 30,000 annually since its debut, 2008 proved a banner year in which sales spiked to nearly 70,000 copies, bringing the total number sold to 311,338. Amazon’s hefty share of that sales pie amounts to 35,000 copies sold in 2008 and more than 65,000 copies sold over the lifetime of the book.

According to Chronicle publicity director Cathleen Brady, Peek-a-Who? has become an Amazon bestseller via “word-of-mouth by customers coupled with the site’s ‘systems’ of having the book pop-up as a recommended title practically everywhere.” The title also appears in many ListMania entries (customers’ listings of their favorite books and products). On its page, Peek-a-Who? has garnered 138 customer reviews, with 114 of those reviews giving the book a most favorable five stars. “The more it sells, the more it’s recommended—a delightful vicious circle!” Brady notes.

While it’s probably impossible to pinpoint the reasons behind Peek-a-Who?’s Amazon trajectory, it hardly matters to young readers, or to those who believed in the book all along. “Sometimes in what seems an act of pure serendipity a book just strikes a chord,” says Victoria Rock, editor-at-large and founding publisher of Chronicle Books’ children’s division, who edited the book. She says that although Laden’s work has many fans, “This little book has definitely carved out a special niche of its own. In these times of so much access to data and so much planning around how to publish a book, it is a nice reminder that publishing is often more of an art than a science.”