There are plenty of activities for introverts. My introvert was a top quiz bowl player, on the Robotics team, fenced, collected insects, went to Davidson THINK, created art that won awards, belonged to the creative writing club, and self-studied for the US Biology Olympiad. She got in to every college she applied to, including some top schools with no positions as team captain, editor, etc. When asked about leadership, she was able to talk about leadership by example, and being a quiet leader. Some of those activities were through her school, but some were just on her own. Worked for her... don't worry if your student is an introvert, just help them find activities where an introvert can thrive.