As an instructor (owner of a space) on rsutdio.cloud, you can create a new project in your classroom space and change it to an 'Assignment': Click on the gear icon, then on the 'Access' (lock) icon, and once you make it available to everyone in the space, check the 'Make this project an assignment' box.
Now, when the student clicks on the project, a copy for the student will automatically be created, but you and the student will both be able to edit any of the files. There's no collaborative editing in the sense that you can't both have access to the project at the same time -- if one of you clicks on it, access is toggled, and the other loses access until they click on it again. Does that make sense?