This fraction teaching tool I have designed is called the Fractionator.
Simply rotate the discs, and read off both the smaller, and the remaining fraction. Good visual guide to teach fractions.
You could also use this as a starting point for teaching equivalent fractions.
I have printed a few test pieces and found that with the original files was a bit tricky to read the fractions, so I've increased the font size on the disks for those of us with poorer eyesight.
Because it is a thin disk, I recommend printing with 100% infill. I printed mine with ABS, however I think PLA would turn out even better. It's a good idea to print each disk in a separate colour.
If you are having trouble reading the fractions in certain lights simply trace the indented numbers with a sharpie.