Period 2: NMAZQQ
Period 3: A4AGMG
Joining AP Classroom is
(1) a requirement to access VQs (see "General Information About AP US DC" on this website) extra credit (see "AP US DC Extra Credit Offers" on this website);
(2) how you register for the AP Exam (you may later opt out [more info at that time]).
Number to call if you're having trouble: 212-632-1780.