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 fail any challenge
4. To shirk (a task or duty).<!--Webster 1913-->
5. 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.)