Reading between the lines ...

I think you might be interested to do this in an object oriented way with a Student and a Course class.

For an object $student you could call a method ->enroll to add a course.

Something like print $_->instructor for $student->courses would become straight forward.

A method $student->timetable would be easily implemented.

And if you decide one day to switch to another representation of the underlying data (like SQL instead of hashes) you'll just need to change the corresponding classes.