Lucidcharts is a great tool with so many great features for use in the classroom to create flowcharts, mind maps, graphic organizers and other diagrams. Their commitment to education is amazing. They offer Lucidchart free of charge to K-12 educators and students. The educational accounts are the equivalent of their team accounts and come equipped with all the premium features. (For other's they offer a free trial, as well as free accounts with limited features.) There product line, support, and tutorials are first class.
Note: Here at Norris, we have this automatically available to all staff and students, via the drop-down menu in Google apps under more:
Lucidchart integrates right into Google Apps and Google Drive. They also have a great Chrome app, and just released an iPad app that is getting great reviews.
If your School (or Business) is Google Apps, then you need to have your system administrator add it to your Google Apps and request the free licenses. More info can be found here.
Their iPad app (Checkout the features here!) was just released, and is a must have free app for teachers and students.
What are you waiting for-- Give this thing a try!