There have been a bunch of people that have asked how to deal with absent students or students that enter the class late. My method isn't perfect, but for the most part I'm happy with it.
When kids are absent, it is mandatory that they make up the notes. Every time I collect ISNs and mark kids off for missing pages, I inevitably have kids tell me that they were absent for a particular day. This isn't an acceptable excuse.
When I make a foldable or take notes I of course make one for myself. I have also started to copy a finished version of it. This is my one for scatter plots that I did earlier this week. Much of it was filled in during class as part of the lesson. I photocopied the completed version to give kids.
The extra copies then go in a filing cabinet. Each course that I teach has its own separate drawer full of folders.
The numbers on the folders correspond to the date on the ISN page.
When kids need to make up pages, I give them my book and they update theirs from it. They use my notebook to get the table of contents, page headings and use the page headings to tell them which folder to look in.
The only issue is when extra copies run out. At the beginning of the year I was making only enough copies for the number of students I have. Somehow this wasn't enough and then I would need to print out extra copies for the kids that needed them. Also the extra copies were blank so kids then had to copy down all the writing. I just don't have enough time for all of this. So instead my new goal is to make the extra filled in copies each morning as I make my new copies for the day. It might require a little extra effort, but having the extra copies makes things easier in the long run.
Update: Many people have asked what to do about kids that enter the class late. For kids that came towards the beginning of school, I had them make up the pages that we had done. Any later than a couple weeks though, and I just have them start their ISN in whatever spot we are in at the time. So for example, if I had a kid enter tomorrow I would just have them start their table of contents with page 16 and keep up from there. They will leave blank pages for the rest of the table of contents and words worth knowing and then start numbering at page 16.