A classroom should include tables or desks, chairs, and black/whiteboards or flipcharts. Rooms like these are normally designed for small study groups.
A classic training session works best with an absence of tables, a loose configuration of chairs, and a flipchart. Training sessions often last for more than 3 hours, so you might want to make sure that beverages are available at the venue (in the form of a water cooler, or perhaps a kettle).