Flunk

verb

1. Of a student, to fail a class; to not pass.

   "He flunked math, again."

2. Of a teacher, to deny a student a passing grade.

   "Unsatisfied with Fred's progress, the teacher flunked him."

3. To shirk (a task or duty).
4. To back out through fear. (Commonly in the phrase 'flunk it', the 'it' referring to a specific task avoided; sometimes without specific reference describing a person's attitude to life in general.)