flunk 
(flŭngk) Informal
(flŭngk) Informal v. flunked, flunk·ing, flunks
v.intr.
To fail, especially in a course or an examination.
v.tr.
1.
a. To fail (an examination or course).
b. To give a failing grade to (a student).
2. To fail (a drug test, as for a performance enhancing substance).
n.
Phrasal Verb: 1. A failure.
2. A failing grade.
flunk out
To expel or be expelled from a school or course because of work that does not meet required standards.
[Origin unknown.]
flunker n.