When you have over 100 students it can be difficult to keep track of who was absent when and what they missed while they were out. To help me keep my sanity, I put most of the responsibility on the students to find out what they missed and how they will catch up.
I have a cork board set up RIGHT next to the door to help manage the system (totally stolen from a former colleague...thanks Forger!) that I use for absent students.
On my end of this system, if a student misses a test, quiz or any other sort of major assessment I immediately write their name on the assessment, put it in a folder (specifically for make up work, color coded by class obviously!), and then write their name (along with the date they were absent) on the small dry erase board near the door.
The reason I keep this board right next to the door is because the students must walk by it before leaving class and my hope is that they notice their name. Obviously I'm actually hoping they already realized they missed something when they were absent, but some students seem to (intentionally?) forget. Again, I also do this so that the students are responsible for coming to me about missing something and I don't have to chase them around trying to get them to make up their work.
Once a student comes to me about their missing work, we work out a time together for them to make up their assignment and they sign up on the calendar below the "You missed something!" board.
This calendar is also placed right near the door as a reminder to those students that have scheduled a time to come see me. On the calendar I also include times/periods that I am not available due to meetings or other personal obligations so that students know not to sign up for those times. This calendar is VERY helpful to me as well because I occasionally forget that a student has scheduled a time with me and it serves as a reminder.
Once a student has completed their assignment their name is erased from the board. This system definitely isn't perfect. Sometimes a student's name can be on the board for days without them approaching me about their assignment. At this point I do have to remind the student that they missed something and get a time scheduled for them to make it up.
When a student does come to make up their assignment (or comes for the extra help they scheduled) I cross off their name and if a student doesn't show up I highlight their name on the calendar. If a student's name gets highlighted I remind them that they were supposed to come see me and reschedule a time. These calendars are really multi-functional because I also keep them after the month is complete and I have documentation of when students have come to see me and haven't come.
Does your school have a policy about the length of time students have to make up work? Is it strictly enforced? How long do you give you students to make something up?