In Transforming School Culture, Anthony Muhammad says,
"Children are not mature enough to understand the ramifications of academic failure; therefore we cannot leave achievement to student interest alone.  In this country, we require individuals to be age 16 to drive an automobile, 18 to vote in an election, and 21 to drink alcohol, yet we regularly give children "licenses to fail" at a much younger age when they do not exhibit immediate interest in academics..." (p. 25) 
In my standards-based grading system, students may re-take parts of the "test" and their newest level of understanding will always replace the old, however the decision to put in the extra time outside of class is up to the individual student.  Is this practice still giving students a "license to fail?"  

When, as K-12 educators, can/should we say, "The responsibility of learning is ultimately up to the student."  In high school?  Never?  The day before graduation?