This Area Assessment is not intended to cover all aspects of the standards for area and multiplication. Rather, it should give a clear picture of areas of specific strengths and weaknesses. It has both straightforward and open-ended tasks that will give you a picture of areas for both individual and group remediation as well as enrichment. Even if students aren't done, I wouldn't have them work on this much past 35 minutes because if it's taking them that long they may be reaching the point of unproductive frustration.
As students turn in their assessments, I take a few moments to glance at them and this helps me plan ahead for what I will go over in the review and reteach. I will not cover all student errors this way, especially since some students will not turn in their papers until the end of the assessment time. I do not need to cover all the errors. Rather, it is important that I direct my attention to problem areas that are emblematic of larger misunderstandings, that I review basic concepts that are still shaky (area is multiplication, perimeter is addition, simply put...) and that at the same time I also ask questions that enrich the students who are ready to move further.