We have not been able to login to the school khan academy account using a chromebook that is logged into his own account, but linked to his school account.

 

We've added his school account inside of his regular family link account -- this is supposed to be the way to do it. The problem is that the "Continue with Google" link is grayed out. This seems to be a bug with either the website or chromeos. As a workaround we add his school account login as a separate user on the chromebook and everything works fine. The problem is that doing it this way bypasses the family link controls so there are no limits to time spent on laptop etc.