Season 1 - 6th Grade

Season 2 - 7th and 8th grade (I can't remember the episode, but somewhere toward the end of season 2, Cory mentions being in the eighth grade)

Season 3 - 9th grade

Season 4 - 11th grade

Season 5 - 12th Grade; Freshmen and Sophomore years of college for Jack and Eric

Season 6 - Freshmen year of college; Junior Year of college for Jack, Eric, and Rachel.

Season 7 - Sophomore year of college; senior year of college for Jack, Eric, and Rachel.


Just to clear up any confusion...