It's possible to block access to personal Gmail accounts with a few creative Blacklist and Whitelist entries.
Add the following URLs to your Blacklist:
Please keep in mind that if Google.com is on your Whitelist this workaround will not work. Google.com will not be blocked by GoGuardian unless it is manually added to your Blacklist or Block All Except Whitelist is enabled. If Block All Except Whitelist is not enabled, it is safe to remove Google.com from your Whitelist.
The Blacklist entries above will also be overridden if you have accounts.google.com on your whitelist. accounts.google.com is often added to the Whitelist to ensure access to Google's SSO login form.
To resolve this conflict, remove accounts.google.com from the Whitelist.
Then, add the following sites to your Whitelist instead:
If some students have already added accounts, you may need to clear cookies on their device so that they cannot simply click on ones that have already been added.