The term was entirely new to me when I moved to Atlanta nearly 20 years ago. In 40 years of living in the upper Midwest, I had never heard the phrase. Seems to make little sense in that, if you are 2/3rds of the way to graduation, you are rising in the sense of continuing toward completion of HS, but what else would you be, “sinking”? In my time not completing HS was unheard of (I recall 3 in my class of 417 dropped out.) I suppose when dropout rates are in the vicinity of 45% in choice school systems like Atlanta, the distinction is necessary. Sigh.
I thought it was an east coast thing. I’d never heard it till moving to the Cesspool of Maryland