Is it usually the case that people's grades go up while they are on rotations their 3rd and 4th years, as opposed to while they're taking classes during their first two years in pharm school?
yes, but most schools have 3 years of didactic and only 1 year of rotations. I did manage to get 3 Bs on rotations, but those were super hard ones that people who just cared about As avoided.
theoretically it's just on your performance. But if someone the month before you, or your month, does a phenomenal job, you probably won't be rated as highly as you would otherwise. Depends on the preceptor too. For the big rotation, drug info (there were 6 of us), grading was very solid. But the preceptor has been doing that rotation for almost 30 years. He has his grading system worked out.