Just want to summarize what most people have said in here in a way you can go back to the school and speak with them about.

1. If he did move the files and change the permissions as they are claiming, then they were not following the Principle of Least Privilege. Least privilege says that a user only has as much access to a system as he absolutely needs. This is the a basic security principle that should be in place ever. If he has more than read access (which is required to move or change permissions) into the google drive then the person (likely a teacher or yearbook sponsor) gave him this permission. That person granting him the access likely violated the schools Information Security Policy.

2. If this access was granted to him by a teacher or sponsor, then it is more likely (arguably) that he made the file move and permission change in accident by a drag and drop error. He was likely meaning to copy the files but instead the drag and drop acted as a cut and paste removing it from the original location.

3. If you went back into that folder and do not have the ability to move the files then they likely went in and changed his file permissions after the fact to remove this access from him. Ask them why he had that access in the first place and how he got it.

4. Tell them that after speaking with a couple of security experts and telling them about the scenario that they said it is far more likely that this was would have been completely unintended based on him being granted too high of privileges within the system, a user error of you will. After all teachers cannot be expected to be computer experts just like high school students cannot. Tell them that you understand the severity of the situation and after a long talk with your son that he does as well. Tell them that you are willing to look past this as a learning opportunity and not push the issue any further if they are. And thank them for their time and concern.

Now, if your son snuck onto the teachers computer and gave himself that permission with her account, or was otherwise able to give himself those permissions inappropriately then this is a much different story. So you need to have a clear eyed conversation with your son and ask him if you need to go to bat for him and let them know that this was not a malicious action and you will under no circumstances accept punishment for the accident and will lawyer up if needed. Or if his actions were not as innocent as he lead you to believe ask him and let him know that you will do your best to minimize damage and work on getting temporarily suspended and not expelled.

As a security expert I can say that kids generally do inappropriate things on computers because they are curious at how things work, not because they are trying to be malicious. Good luck, keep us updated on the outcome.