888-225-5427
(toll free in the United States and Canada)
More information on how to access your College Board account:
If you forgot your password:
https://support.collegeboard.org/help-center/i-forgot-my-password-how-do-i-reset-it
If you receive an Error Message 400 when trying to login to your AP classroom, try this before calling College Board:
Clear your browsing history by clicking on 3 dots, go to settings, and select privacy and security and clear browser history. Then select delete all and restart your computer.