I think progress reports are one of the most efficient methods of assessing students within the classroom. Progress reports don't have to have grades associated with them and offer insight into what a student is doing well or needs to improve. Progress reports also always parents the opportunity to understand how their child is doing in the classroom.
In my old school district, our progress reports included our current grade, as well as comments. I liked this type of progress report because it not only gave a grade but it explained how you attained that current grade and how you can approve it.
An example of this (and yes, this is from one of my old progress reports in high school) is:
Subject:
European History AP
Grade
B-
Comments
2, 5, 13
Comment 2: Participates well in class.
Comment 5: Does well on tests and quizzes.
Comment 13: Student is missing a few assignments.
Based on that progress report, I knew that in my history class, I was missing a few assignments so I needed to hand those in as soon as possible to increase my grade.
As a teacher, I would definitely use progress reports more frequently than each marking period. Instead, at the end of each month, I'd assess my students and send home progress reports with their journals. If teaching kindergarten or first grade, I would probably complete progress reports more frequently than once a month; probably twice a month or weekly. I wouldn't, however, attach a grade to the progress reports unless a student was doing poorly or exceptionally well and the parents needed to be aware of this.