Figuro is a free, online 3D Modeling App.
It is not DoDEA approved but it can be utilized without creating an account.
If a student begions a project, they can leave the window open and it will be available for further editing (if the student uses the same device).
Here is a link to a short 5 minute tutorial of the basic features of Figuro:
How to Use the 3D Tools of Figuro