A leader is just a good follower that sticks with something (club, sport, community service, or academic subject) and is ready to step up and take a more pronounced or active role as a junior or senior. Sometimes the opportunity presents itself and can be taken . . . and sometimes not. But if a student is not continually active in something specific, or does not seek out a community to be a part of, then the opportunities to show the leadership desired by colleges will be few. My feeling is that it is best to try to find some activities that a student can pursue for all 4 years of high school. At the end of that time, hopefully there has been a chance to show leadership. If not, there has at least been the opportunity to show commitment to something. And commitment is probably as sought after by colleges as “leadership.”
At first it may seem that leadership is connoted by titles like “captain” or “president.” This can be frustrating, if you are not athletic or “popular” enough to be voted into a more public leadership role. But leadership can be shown by becoming a math tutor at your school or in your community by organizing meals to be delivered to needy families through a church. One of my kids has studied Latin in high school and has gone to pretty geeky Latin festivals, but just by participating in such events has almost accidentally become a leader/tribune for her class. And Latin is pretty much known for introverts. So there are opportunities out there for all kids.
I would avoid the negative comments about club presidents doing very little. On occasion, I have known of officers of misc. clubs being asked to tutor struggling students before or after school or coaching a school’s academic team before an interscholastic competition. This is often done quietly and without publicity or fanfare. Also, I have known team captains that have organized summer practices and who have had to address questions of drinking or worst among their peers. Often these leaders are people that the high school administration relies upon in unseen ways. Just encourage your kids to be involved in school and/or community activities and they will find their own ways to demonstrate leadership when you least expect it. 