According to Wikipedia: "Margaret Penrose was a house pseudonym used by the Stratemeyer Syndicate.. The Stratemeyer Syndicate was the producer of a number of mystery series for children, including Nancy Drew, the Hardy Boys, the various Tom Swift series, the Bobbsey Twins, the Rover Boys, and others. 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 USA were Stratemeyer Syndicate books, based on a 1922 study of over 36,000 children country-wide."
According to Wikipedia: "Margaret Penrose was a house pseudonym used by the Stratemeyer Syndicate.. The Stratemeyer Syndicate was the producer of a number of mystery series for children, including Nancy Drew, the Hardy Boys, the various Tom Swift series, the Bobbsey Twins, the Rover Boys, and others. 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 USA were Stratemeyer Syndicate books, based on a 1922 study of over 36,000 children country-wide."