Calling itself “The Front Page of the Internet,” Reddit is basically a massive discussion forum: Users post links, comments, or questions, and other users can comment on a post and vote it up or down, which gives the post a score and ranks it among other posts. The highest-ranked posts appear at the top of the page. Posts can be submitted to the general feed or to a subreddit, a smaller community focused on a specific topic. Users can also purchase coins they use to reward others for good posts.
One popular feature is Reddit AMAs. Short for Ask Me Anything, these threads allow people to present themselves for public questioning of any kind. This includes celebrities and public figures.
Teenagers seem to be into Reddit and teachers should have some familiarity. 
Even though Reddit is chock-full of information and entertainment, be cautious on using it at school. Limited moderation equals inappropriate content, so unless you work in a really permissive community, parents will balk if they hear you sent students to Reddit for research. But definitely check it out yourself!