Ivy: Ivy practiced the charm. Although she was muggleborn, she was incredibly studious and a fast learner, so she was very good at magic and was used to being top of the class in most subjects. She cast the charm and smiled at her success.
Veronica: Veronica frowned as she tried casting the charm again. This was not her area of expertise. As she was and had been teaching herself to be a healer, her best subject was Potions, and she excelled at healing spells. She was a good student, so she did okay in everything else, but wasn't amazing.
Lucas: Luke cast the charm and grinned as he cast it perfectly. Luke had always had an affinity for learning and perfecting spells rather quickly, so he excelled at Transfiguration and Charms. He had been told hew inherited this from his parents, and every time he perfected another spell, he had to smile and thank them in his thoughts.
Alexei: Alexei cast the charm again. Although he could always remember the incantations, he wasn't always top-notch on the spells. Alexei had an amazing memory, he basically had to hear it once or twice and would remember it years later. This meant he was great at theory, and anything where they had to analyze, study or memorize information, such as History of Magic or Ancient Runes. However on the practical scale, not so much.
