Sometimes, when Dionne Hammiel wants the attention of her rambunctious kindergarten class, she stands on the table. Other times, she lowers her voice to a whisper, making her instructions a very important secret that every child strains to hear. The hushed message at John Burroughs Education Campus in the District was utterly routine on a recent day: “We need to go to the bathroom, drink some water, come back, and pick out our books to…