Hi, David.
There are a number of reports that a teacher/admin can view to see the activities of an individual student. When viewing a student's profile, check out the Activity reports under the Administration menu. There's also reports about students participation in Forums, Quizzes and Blogs.
As for seeing activity "for each login to the system", there is nothing that I know of that will make this distinction. The trouble is distinguishing the time window of such a session in the asynchronous Web. I suppose you could mark times the student has logged in as the start of such a time window, but as that session can persist for days, determining the end of such a time window would be difficult.