Hi Starbut1,
Please correct me if I am wrong but I believe the rooster import you mentioned is more designed at American MIS, they basically do the same that Wonde does for you.
If you are the administrator of your Google Tenant then there are a couple of ways I would action this.
First way is to use a free tool like https://educ.io/classes/. You'll need to give it permission to access and action items on your behalf. As a super admin you will be able to search across all your tenant classrooms, or filter by teachers to find their classrooms (same for students). You can then remove the class you don't want to action anything on from the list. You can then go t add (force) the students to be members of the class or invite the students by pasting their emails in, you can bulk paste too.
Second way is GAM. At first GAM seems... overwhelming but once you really start to use it, you'll wonder why you didn't use it in the first place. You just need to find the classroom ID, then your code would be something like
gam course (the id) add student
[email protected]
I would then put this into a spread sheet, concatenate the students emails, copy all the lines of code, dump into GAM and watch the magic happen.
The final way is to leveage your admin account with Classroom. You should be able to go to Classroom, use the Admin Tools to find the class, and temporarily gain access to the new classroom. You will still be inviting the students but then all they have to do is accept.
I understand the reluctance to use, however I regret not using it earlier in my Google Management. https://sites.google.com/view/gam--commands/home is fantastic source for getting codes.
I hope this helps.
-Tom
