Mcgonagall and Slughorn had allowed the group access to the dungeon’s for the rest of the year as a safe place to transform since no one was allowed outside after dark and they couldn't very well morph into animals in daylight. She had extended the ceiling so Draco was able to shift but not fly or move much. He practiced switching forms over and over until he could do it in the blink of an eye, going back and forth between the two with complete ease.