Portal Visitor permissions

Is it possible to set up Portal Visitor permissions? Like Portal Visitors can only view records assigned to their Portal Visitor Name. For example, School Test Scores. I only want a portal visitor (Student) to be able to view their own test scores. I don't want Student A to be able to go to the View Test Score portal page and change the URL from &id=11115 to &id=11116 and then be able to view another student's test scores. Another issue I have is that if I have two separate portals. One for Students and one for Teachers (the teacher's portal lists all related student scores). If a Student logs into the Student portal, they are now a "Logged in Portal Visitor". If the student somehow found out what the URL is for the Teacher portal, all they have to do is visit the URL and they are granted access to the Teacher portal. They are considered "Logged in Portal Visitor" even though they logged into a different portal. One solution I came up with is to use one portal but use formulas to display information bas