The remainder of prisoners needs must also be kept as low as possible to maximise a prisoners concentration: Keeping a safe, well guarded environment will keep the demand for weapons etc.
Similarly, the more general sense of law and order there is within your prison the less punishment will be dished out (which adds to suppression). This means it is helpful to keep armed guards away from the classroom areas. You've already identified that suppressed prisoners do worse in programs because they are less willing to learn. Understanding is specific per prisoner, some prisoners are as you say not academic enough to do well in basic/general education courses.
Success in reform programs is defined by two factors - a prisoners understanding of a subject which you can not change and also a prisoners concentration on their studies, which is related to their needs.
