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Twitter is a simple and popular social network that is free to join and easy to learn.  140 character pieces of information called "tweets" are posted by Twitter users all over the world.  By "following" someone on Twitter you'll be kept up to date on all of their tweets, which can be anything from simply their thoughts to pictures to links to all kinds of articles, videos, and really anything on the internet.  

Twitter is already widely used by many teens.  In a highschool setting, Twitter can be used by teachers and students to streamline communication and make it possible for students to ask questions whenever they need to.  A biology 30 teacher could make a "Mr./Mrs. Smiths Bio 30" Twitter account and tell all of her students in class to follow the account.  The teacher could then tweet links to articles or YouTube videos relevant to that day's lecture material.  Updates on upcoming tests and assignments could be posted regularly to ensure students aren't showing up to class with incomplete work or without having done a minute of studying.  Furthermore, a student having problems with a question on the homework is one tweet away from their teacher's help at any given time. 

With Twitter being social in nature, the website could be very helpful for students who learn best in a group setting.  Discussions involving multiple students can easily be started, as a student may have something to add to another's question, and another student may join in with what they think is the answer.  Soon a group discussion is well underway and examples can be talked through and explained in several ways.  Twitter also allows for the use of various media, such as video and pictures, appealing to learners whose optimal situation is not sitting in class  hearing a lecture.  

There is no age limit to join Twitter.