How did Maya, Riley, Lucas, and Farkle go from being in 9th grade to suddenly being in 11th at the end of the show?

I've just started streaming this show on Disney+ and in the 3rd season they're just entering 9th grade high school. At the start of the show they're all in middle school doing 7th and 8th grade so yeah I don't detect any sudden time jumps as far as I can tell.

Unless there's a sudden time travel episode where they jump ahead that I've not aware of.

double post