Realistically speaking - no one in college is going to stop after the end of every class (before getting up to go to the next class, back to the dorm, out to lunch with friends, etc.) and make a backup of whatever notes that were made in that class... whether it's to an external hard drive, a flash drive or even a separate partition on the internal drive... at least not for very long - even with the best of intentions.
Creating a copy of a file on the same drive... whether in the same partition or a separate partition...
is not a backup.
Slydude summed it up best.
1 external drive with 2 partitions
1 with a bootable clone via CCC which will permit the computer to continue to be used in the event the internal drive dies
1 using TM which will permit the restoration of deleted &/or older versions of files which could be useful in school work
... Once Time Machine is set up it looks for the external drive to perform a backup. If that drive is unavailable the backups are stored on the internal drive until the external drive is reconnected
The above is automatic - once TM is set up, there is nothing further for you to do - it silently creates backups once an hour without any further interference from the end user. If it is not connected to the drive that has been set up for it to use, it keeps these backups on the internal drive. Once connected to the TM drive, it will auto transfer those backups.
The problem chscag mentions, is that if she does not take the time to connect her Mac to that external drive with regularity - preferably once a day - to allow TM to transfer that data to the external drive - then she could fill up the drive with these backups and cause a whole other problem.
Once the TM drive gets full - it also auto deletes the oldest backups to make room for the new ones.
CCC is not automatic and will require the user to launch the app and update the clone.
(And most of us are "still" PC guys. Even in a Windows environment, I could not in good conscience recommend, nor is having a copy of a file on the same drive a "backup".)