I am having exactly the same issue. As a teacher I was able to pull all, but one student into the Khan Academy class via Google Classroom. The student and I also entered the class code, but again we received a message stating that the parent access on the account (which shouldn't be because it is a school account) is blocking the student from joining the class or adding coaches. I also tried emailing the student's school Gmail account to invite him that way and similar problem. I even contacted the parent and she confirmed that she did not have any access to the student's Khan account. 

Hello- I have also experienced these frustrations in my classrooms.  I know that may parents do not fully understand that a school account belongs to the school and not to the student and they sometimes go in and make changes that they don't fully understand.  Generally, when you look at a students account settings (once they are logged in) you should be able to click on "Settings" and see any emails that are attached to that account.  If a parent email is listed- then they MUST have linked it at some point.  They will need to try to log into Khan using their parent email - and might even need to request their password if they have forgotten it.  Once they have access to their own account they can go adjust settings to Allow Other Coaches in the Child Accounts.  Then the Child should be able to add you as a coach.  

If this will simply not work, you can also simply create a new account for the student.  They cannot transfer their progress and they have to "start fresh" - but it has provided us a good "learning opportunity" for many of our students and parents when they take control of an account that was not theirs to take control of in the first place.  We look at it as a good lesson in Digital Citizenship. 

Does this help at all?  Let me know! 

Julianne Russell

Boise, Idaho