Until moodle 2.8 only the teacher can share a study material among the students . however, this latest buzz called 'Social learning ' booming very frequently all around the world.
for now core plugins like my private file facilitated the students to store and maintain their favorite study material with in moodle . but i feel if its an interesting material for a student , then it might also helpful for another student who following the same subject . therefore , its better that the private files block have an extra features to share the files among the student .