Flock is a great pick for students who want to communicate with their teachers and fellow students on-the-move. Not only does it help in chat, but also helps you stay on top of your projects at all times. Have a query - just video in your pals. Share assignments and interesting articles on the move. Flock can also act your notification hub from other apps.
Easy to use, free for students and available across platforms, this one should be on your must-have list!