Consider a class of students that are blogging. By merging a set of student blog feeds, say of a Math Journal, into a single feed a teacher can get a feel if the content that you are trying to delivery or the point you are trying to get across in your classroom.

You might also be able to identify gaps in the knowledge of these students and see what is specifically interesting to them in the classroom.

Finally, it is just convienent to have all the feeds aggregated in a central location for both you and students to view new postings.

Take a look at http://allrss.com/rssremixers.html for a list of RSS Mixers.