Answer: Island Heights.
Prior to the formation of the camp, some years earlier, Wanamaker had established the John Wanamaker Commercial Institute. He formed this "store-school," as some came to call it, as an educational facility for his workers, particularly those in the younger set. (The U. S. didn’t see the establishment of child labor laws until the early 1900s.) The school taught traditional classes like reading and grammar, and offered specialized classes in subjects such as hygiene, accounting, and upholstery.
Camp Wanamaker was borne out of Wanamaker's wish to provide summer vacations to those involved in the Commercial Institute. For two weeks a year, students attended the camp at Island Heights, New Jersey, where they practiced military drills and participated in drum and bugle corps. Camp Wanamaker became a highly-organized outfit, and some of its graduates went on to serve in the U. S. Armed Forces.
HSP's collection of John Wanamaker records (#2188) contains some papers, publications, and photographs relating to the John Wanamaker Commercial Institute and Camp Wanamaker. Among the records are also those relating to Wanamaker's efforts to educate his employees.