Flunk Out Meaning

(idiomatic) (of an educator or institution) To impose failing grades on (a student), often requiring a retaking of the course or academic year.

Example:   He flunked out of high school as a youth, but finished school later in life.
1974, Robert M. Pirsig, Zen and the Art of Motorcycle Maintenance:
  They could simply have replied, "No, we're way too square. And until you do come up with an answer, stick to the syllabus so that we don't have to flunk out your mixed-up students when we get them next quarter."