In the military it is quite easy, although getting the higher paid help to agree is sometimes difficult.
Throughout their training all student sorties are written up and an objective assessment of performance made. The student gets a copy, which they sign and nothing can be added to the original. All shortcomings are recorded in full. Further, regular reports are raised (fortnightly/monthly) which are commented on by CFI and Squadron Commander and again signed by the student, thus ensuring adequate supervision.
If a student is not achieving the objective standards they are interviewed and debriefed on their shortcomings and given a remedial training package that should result in them achieving the standard. Further failures result in a more formal warning and leave the student in no doubt that they are not making the grade. Ultimately they are informed that a trip, if not passed to a satisfactory standard will result in suspension from training. Failure results in another sequence of events.
At this point they are wheeled into the office to receive the pronouncement;
"OK Bloggs, what does your mother call you?"
"Martin sir."
"Well Martin, you're chopped"
No further ceremony is required - we've buried enough who were given the benefit of the doubt!