We usually do all of the reviews and practice assignments, but occasionally I'll assign one as it comes up and assign another in between the next regular lessons. Sometimes they are a bit overwhelming. It's not unusual for there to be three very long review/practice assignments all at once. As far as how to write them out, my DD, gr 3, likes to write them out on a separate sheet; my DS, gr 2, does not. I use sheet protectors and slice open the long side, slide it over the page, and hand over a dry-erase marker. Sometimes there are too many problems for even that to work though.