Lucidchart is different from other mind mapping sites that I've used before because the interface is based on dragging and dropping elements into the workspace. It is as simple as selecting what you want from the menus and then dragging and dropping them on to the canvas. Everything is then easily resized or edited. Check out the video below to see Lucidchart in action. H/T to Richard Byrne for the video.
For many students, the best way to understand something is to see it visually represented. Lucidchart is a great way for those students to work either at home or in school to accomplish that visual element. For teachers this is a great tool to clarify difficult/convoluted topics in class.