As a prefect, it was Hestia's duty to provide the best example that she could. For her, that meant displaying hard work and devotion to her studies in a respectable manner. Showcasing one's potions skills in a (hopefully) friendly competition would be one step towards achieving this image.
She tried not to think too much about what the other students were doing. At the moment, that was the referee's job. Instead she concentrated on making sure she got accurate measurements and percise timing for her own potion.
She tried not to think too much about what the other students were doing. At the moment, that was the referee's job. Instead she concentrated on making sure she got accurate measurements and percise timing for her own potion.