Some definitions that may help deciphering the above:
PO = Performance Objective
Each military course is divided into Performance Objective (think of these as individual subjects). Each PO is further divided into Enabling Objectives (EO). PO and sometimes individual EOs, are confirmed by Performance Checks (PCs, i.e., tests). There is no concept of "averages" for performance, you can't fail some things and make it up on others, each Performance Check has to be passed to complete the course.
PRB = Performance Review Board
A Performance Review Board may be conducted on a student that is failing to achieve the Performance Objectives (or for other reasons like discipline and attitude). The PRB will determine if the student is likely to be able to complete their current course, with or without additional assistance as possible within the existing timetable and resources, or if the student is best served by being removed from training and placed on a later course serial. If recoursed, a student may be held to restart the new course from the beginning, or if other courses are underway and it is considered a workable option, the student may be sent to join another course already in progress. If the PRB determines that the course material is beyond the student's grasp and they are unlikely to ever complete it to the required standard, then release is a possibility.