The main goal if I understand is that student actually understood what exercise asked him to do. Typically, if a student did not understand what exercise is about - it will clearly be visible. There is a section of "mistakes", which are good indicators that a student requires a little more pages. Generally, I'd first look at mistakes section and seek for some. After that I'd compare the actual work with example homework to spot any things that'd indicate the lack of understanding of the purpose of the exercise. Or the lack of actual effort (scribbling). But this is just my opinion, I didn't do any critiques on the community platform yet! Derived it from common sense and what Uncomfortable says in lesson zero about that student shouldn't get a perfect work done, but should complete it with a general understanding of what is going on and move forward with these concepts in mind.