This is an interesting thought. I think setting up a simple LinkedIn profile is probably a good thing for just about everyone, including students. Originally, LinkedIn was conceived as a business networking site. Then, it became a heavily-used recruiting and job search tool. A few years ago, LinkedIn began encouraging college students to set up profiles to be ready for job searching as they complete their degree. Kind of amusing to see it pushed all the way down to high school now, but I get it.
The benefit I see is that your LinkedIn profile is a positive, controlled search result if someone “googles” you. It will probably be one of the top results (depending on how common your name is and other factors). You control the headline and the content. And, once it’s there, it can be updated throughout your college years as your focus shifts to internships, part-time and summer jobs, etc.
I really can’t imagine the vast majority of schools digging deeply into the social profiles of their applicants, but LinkedIn is part of working life these days and it won’t hurt to get started. And, at those selective schools that take a hard look at applicants, I don’t doubt that sometimes they do turn to the Web to build a more complete image of the student.
Once in college, I’d recommend removing all but the most significant high school content. It’s a lot like your resume. When you are applying to college, your high school accomplishments and activities are important. Once you are in college, though, nobody cares about that stuff.