Margaret Penrose was a house pseudonym used by the Stratemeyer Syndicate. The name was used for: The Dorothy Dale series, The Radio Girls series (Later reprinted as The Campfire Girls series), and The Motor Girls series. The Stratemeyer Syndicate was a publishing company that produced a number of mystery book series for children, including Nancy Drew, the Hardy Boys, the various Tom Swift series, the Bobbsey Twins, the Rover Boys, and others. They published and contracted the many pseudonymous authors doing the writing of the series from 1899 through 1987 when the syndicate partners sold the company to Mega-Books. Created by Edward Stratemeyer, the Stratemeyer Syndicate was the first book packager to have its books aimed at children, rather than adults. The Syndicate was wildly successful; at one time it was believed that the overwhelming majority of the books children read in the United States were Stratemeyer Syndicate books, based on a 1922 study of over 36,000 children country-wide. Stratemeyer's business acumen was in realizing that there was a huge, untapped market for children's books. At a time when most children's books were aimed at moral instruction, the Stratemeyer Syndicate specialized in producing books that were meant primarily to be entertaining. In Stratemeyer's view, it was not the promise of sex or violence that made such reading attractive to children; it was the thrill of feeling grown-up and the desire for a series of stories. Stratemeyer believed that this desire could be harnessed for profit. He founded the Stratemeyer Syndicate to produce books in an efficient, assembly-line fashion and to write them in such a way as to maximize their popularity. The first series that Stratemeyer created was The Rover Boys, published under the pseudonym, Arthur M. Winfield. The Rover Boys books were a roaring success: A total of 30 volumes were published between 1899 and 1926, selling over five million copies. The Bobbsey Twins first appeared in 1904 under the pseudonym Laura Lee Hope, and Tom Swift in 1910 under the pseudonym Victor Appleton. Less