I ended up using recycled file folders and dry-erase contact paper to make these re-useable dry erase folders. They were a huge hit.
To make the folders, I cut off about 2/3 of the front flap of a file folder. The inside of the back of the folder is now exposed. I covered it with a small sheet of dry-erase contact paper. I found a big roll online for about $20. There is enough in the roll for 60 folders, so it will last a long time.
I cut the remaining portion of the front flap into tabs, one for each problem. I lifted up each tab and wrote the solution underneath. This took a long time. Next time, I will try to use a set of problems that I already have typed up. On the up side, it is a one-time thing. These can be re-used again and again and again.
Now students can work out a problem in the dry-erase area.
When they are done, they can flip up the tab and check the answer.
Then erase and move on to the next problem.
My students really loved these. Since I had made multiple versions, they asked if they could take home an extra one for practice.
In the future, I can envision a file crate full of these . . . labeled by skill . . . so that students can just grab and work on whatever as needed. It hate to think about making all of those, but I it just might be worth it.