(Portland, OR)  --  Officials with the Portland Public Schools district are warning parents that students may stage more protests this week.  Students held peaceful protests last week, but police say it appears "outside organizations" are encouraging middle- and high-school students to participate in further protests this week.  The school district sent parents a letter issuing the warning.  The letter states the police are concerned about the safety of students if they join any of these outside organizations in their demonstrations.