Dunwoody High School teacher Thenita Williams, standing, goes over math problems with 11th graders Brandi Thomas, at left, and Chelsey Allen. Dunwoody’s math classes started the winter term in new, state-of-the art classrooms built as part of a renovation of the high school. A dozen math classrooms and a mass communications lab were opened at the completion of the second phase of the renovation work, Dunwoody Principal Rodney Swanson said. The first phase of the work, completed over the summer, added new heating and air conditioning systems, new science classrooms, new lights and expanded the cafeteria. The final phase, to be finished in the spring, will add a 500-seat theater.