I decided to adopt this Classes workflow this year, as the Moderate Kids functionality becomes unstable when I am working with hundreds of students. I didn't realize the nightmare the Classes feature would create when getting the students started there. I am an out-of-classroom teacher, and see hundreds of students. Some of these students are using Tinkercad in more than one setting, not just the class I created for them. There is no way I am going to create two accounts for the kids for two different classes, their work should reside in one location. Some of these accounts had previously used the Google SSO option, I hope that doesn't create an issue when you work out a way to transfer students to other classes. But, for now it looks like I'm going to have to go back to Google SSO instead of Classes until you figure out how to move students to other classes, and allow a student account to be in more than one class simultaneously.