The ISP allows time to build confidence by mastering material before proceeding to the next stage. Students must be able to set reasonable time schedules for themselves and hold to them with effective study. They must discipline themselves against outside distractions and procrastination. The fact that they can postpone taking an exam is often counterproductive for making reasonable progress. The fixed scheduled exams of the lecture program are great motivators to study.
Some students just do better with such a schedule.
Compulsive students often move too slowly. The time freedom works just the opposite on the compulsive students. These students feel that they have to learn everything and accordingly do exceptionally well on exams, when they finally get around to taking them. They can be constantly behind schedule and then out of sync with other students. This leads to problem 3.