When I was in the regular classroom in Idaho we had a scripted curriculum with tests every Friday. The test would take students probably around 45 minutes. I would grade papers while they were working. I still kept an eye on them and got up about every 5-10 minutes to walk around and make sure they were getting their work done. But I didn't feel the need to keep walking around when they were doing an independent test. No one ever seemed to have a problem with this.