Now in its 40th season, Circus Flora is preparing to take its audiences on a journey back to high school with its “Flying High” show. Opening June 4, the show will feature a variety of acts across “classrooms” of acrobats, aerialists, clowns and more — including many of the acts that have made the circus a mainstay in St. Louis for generations. Jack Marsh, the circus’s executive director, called the anniversary an “incredible” milestone.